Now, would you care to name a piston twin which does not have a postive rate of climb at MTOW if properly rigged and flown. I do not know of any.
I have flown a number of Seneca IIs that have not exhibited any rate of climb and not even at MTOW. The book figure reflects a new aeroplane not one that has been around for a few years.
Ok. I'm sure you're right.
I am not saying this would apply to the Seneca but I know of several Beech twins that were climbing less than advertised on one engine until the owners got them properly rigged and cleaned up. Some of the owners reported as much as 100 feet pr minute increase afterwords.
This topic does run and run.
I have had lots of engine failures in twins and every time I have landed quite safely on a runway at minimal risk to my passengers.
In most twins which are used seriously (ie not just as trainers) the MTOW EFATO case is quite safe if handled within a reasonable tolerance. My Aztec actually does (ie I have tried this for real at MTOW) better than 400fpm. I have achieved double that on a very cold day.
The vital thing is to feather the dead prop. Steve C and I tried an experiment a couple of years ago, trying to keep flying without feathering, and the result was a slight climb, but a complete impossibility of keeping straight.
The answer to the single hydraulic pump on the Aztec, in my opinion, is to whip the gear up as soon as you are airborne. There are disadvantages to that, of course, as the option to land straight ahead is lost, but as, with the gear up, the aircraft will keep flying and climbing, it seems the lesser of two evils.
I'm surprised the "is a twin safer than a single?" took this long to surface on this board. Apparently the posters are quite restrained. 
For "average" recreational pilots (like myself), I would always suggest a single over a twin, unless you're willing to spend a lot of time staying both current and receiving regular sim training on emergency procedures. It takes a lot of discipline handling a twin, in addition to extra systems complexity, especially if you're upgrading from a fixed gear a/c.
Also treat every single departure as special; do your pilot briefing, balanced field calc, rotation speed, climb-speed, climb-out options, and stick to your decision points, and always expect one of the damn engines to quit below 500 ft AGL.
Departures aren't the only concern. Arriving single-engine does require your full concentration as well. This horrific tragedy in 2011 involving a C421 (7 people killed, incl 5 children) shows what happens if you make a couple of mistakes in the end-game, in this case adding full flaps [too early] on finals. The pilot lost his RH engine in FL210 cruise, and did an emergency landing at an unfamiliar airport at night; what should have been a "routine" emergency, ended up with a fatal accident:
http://www.ntsb.gov/aviationquery/brief2.aspx?ev_id=20110710X31135&ntsbno=ERA11FA391&akey=1
Having said that, knowing the limitations of your own aircraft (try the "drag demo" to get a solid feel for your single-engine performance) & regularly keeping sharp on the emergency procedures goes a long way. I definitely feel more comfortable flying in a twin. Then again, I fly in a region with rough terrain, a lot of open ocean, and few airports. I may feel differently in a more GA "friendly" region.
I have had lots of engine failures in twins and every time I have landed quite safely on a runway at minimal risk to my passengers.
I guess the thing is, that we don't hear about those who make it. We only hear about those who didn't...
Performance on one engine is a big part of multi engine operations. On hot days at high airports with terrain issues even jets are frequently performance limited, and analysis of the figures will often mean you have to consider going at lighter weight or at a cooler time of day. I doubt many piston twins are realistically usable at some of these places. Thankfully not too often a problem in the UK, but in mountainous areas of Europe it can come up, and in the US it is more common.
There are quite a number of European SIDs, in mountainous regions, whose gradient is well above 500fpm.
Some I have seen would be very tight for the TB20 if one is concerned about CHTs.
Obviously that is not an argument against a twin because a single definitely won't achieve the required gradient after an engine failure
Some of the owners reported as much as 100 feet pr minute increase afterwords.
I don't doubt it.
Having spent most of my time in twins teaching asymmetric I am only too aware of the differences. If you own a machine you want it to perform at its best, but when training you finish up with the cheapest beast you can find. That's not necessarily a bad thing because its better to teach energy management in a device without any, than one that performs well. The 2 and 3 bladed Senecas are quite different and surprisingly I always managed to get a positive ROC out of the lower powered and lighter MKI. It is however an aircraft where the decision to land needs to have been made before you roll; if the numbers are not in the window you are not going anywhere as demonstrated at Newmarket a few years ago.
Twins spend a very small amount of flight time where asymmetrical thrust is a significant safety issue. Most of the time is spent in the flight regime where the redundancy is a safety benefit. Dual engines, dual alternators, dual vacuum systems are a big plus when flying over inhospitable terrain or water or in IFR conditions. Training reduces the risks during the departure and approach phase, but it doesn't eliminate them.
Performance on one engine is a big part of multi engine operations. On hot days at high airports with terrain issues even jets are frequently performance limited, and analysis of the figures will often mean you have to consider going at lighter weight or at a cooler time of day. I doubt many piston twins are realistically usable at some of these places. Thankfully not too often a problem in the UK, but in mountainous areas of Europe it can come up, and in the US it is more common.
You are no more limited with a piston twin that operates out of a field that doesn't permit single engine climb than you are with a single engine aircraft. Using the logic that this prevents use of a twin in mountainous areas would also prohibit use of a single engine aircraft.
Commercial use is a different matter. In the US, commercial operators at high altitude airports are often unlikely to be able to make an engine out climb and follow the Obstacle Departure Procedure. They then to design their own "escape plan" in order to operate from these airports. Engine out consideration is not provided in procedure design.
I think this is a pretty civilised "twin thread", compared to some I've seen elsewhere.
But it's worth asking why this topic generates so much debate among pilots.
IMHO, the reason is that the "twin route" is nowadays so much more difficult and costly, so everybody not flying a twin - myself included - is trying hard to justify why they aren't flying a twin
The paperwork is harder to get, and considerably harder to keep (annual checkrides etc especially in Europe)
The operating costs are way higher. The fuel is the biggest chunk in Europe, and that is about 1.8x higher, for maybe 10% extra speed. Obviously direct comparisons are hard but there are some where the airframe is similar e.g. PA32 v PA34R?). You also get screwed everywhere else down the line e.g. hangarage, landing fees...
For those who like modern hardware, there is far less choice in twins - apart from the DA42 which itself comes with some pretty sharp tradeoffs (unless you totally ignore the company history).
Evidently, the bulk of the piston GA market has already voted on the above with their feet which is why almost nobody is making piston twins today, which is unfortunate.
The other really unfortunate thing is that turboprop engines are not coming down in price. However, if they were cheap, almost nobody would be buying twins Well, apart from European AOC (charter) ops which still have to operate a shagged old twin, as a minimum.
