Not sure about the GTNs but outside controlled airspace it would be great to be able to fly say 2nm to the right of the GPS track.
Currently one has to do it by flying in HDG mode.
The purpose is to avoid flying into somebody 
The GTN has this - I use it a lot, particularly when flying between busy VORs (OCK-MID-BIG-DET etc).
The turns are nicely rounded off for you, and as long as the angle isn't too acute it works very well.
On a few occasions I've seen traffic pass by exactly where I would have been, a mile or so to my left. In my mind this does more for collision avoidance away from the circuit than a TCAS.
I suppose this mainly applies to those without a touch screen. With a touch screen you might not bother using VOR's or IFR intersections, and simply drag the track to whereever you want.
I've not felt the need to date, but can absolutely see the point.
My solution on the other hand, and probably the reason that I haven't felt the need, is that I almost always fly to/from a convenient but semi-arbitrary landmark close to both my departure and arrival points.
On the other hand, it does make backing up navigation using other radio navaids relatively problematic. Cross-checking workload is much lower if the magenta line, and the VOR CDI co-incide. On the other hand, that's also soluble - fly from a point a few miles from your start point TOWARDS a navaid (useable with VOR or deities-forbid even ADF), rather than directly from the start point. Then switch to another navaid some distance short of the honeypot-beacon and track towards that using both GPS and VOR/ADF.
That said, in reality I don't think I do this either - I pick a route, which is seldom a true straight line as I wiggle around class A, mountains, danger areas, etc. Then I work out how to make the navaids support that. Doing it that way, I don't find much risk of anybody being on my reciprocal route.
G
The flying of lateral offsets is really something for areas with poor or no radar coverage. Here In central Europe, controllers expect you to fly as precisely on your assigned track as your navigation equipment permits.
Flying IFR outside controlled airspace (which is verboten anyway in our part of the world) I would rather fly random point-to-point courses than parallel to some airways above that don't apply for me.
I don't know about other manufacturers, but with Garmin, the newer "W" (WAAS) models support parallel track offsets.
Flying IFR outside controlled airspace
Why IFR?
It is 100% legit to fly any track at all in Class G, VFR, and picking a VOR-VOR-VOR route means one has an instant VOR/DME backup for a GPS.
There may or may not be a published airway on that track, in the CAS above.
(which is verboten anyway in our part of the world)
Germany, maybe, no IFR in Class G, but from what I hear not for much longer
It is 100% legit to fly any track at all in Class G, VFR, and picking a VOR-VOR-VOR route means one has an instant VOR/DME backup for a GPS.
I would say, when flying VFR, the GPS is my backup for visual navigation. I need no second backup to backup my backup. In twenty years of using GPS, I have not yet had a single GPS failure BTW! But VFR, I fly and also teach to fly the shortest possible route from A to B, that's what the aeroplane was invented for, wasn't it? I never undesrtood why people would plan VFR flights via ground based navaids and airfields - that's a sure recipe for close encounters with similar minded flyers...
But VFR, I fly and also teach to fly the shortest possible route from A to B, that's what the aeroplane was invented for, wasn't it?
I never undesrtood why people would plan VFR flights via ground based navaids and airfields
This is going to be a long day
Parallel offset is a requirement in the specification for a WAAS GPS. TSO C145/146 as required by RTCA DO 229C/D. From DO 229C:
2.2.1.3.16 Parallel Offsets The parallel offset is defined as a route parallel to, but offset from, the original active route. The basis of the offset path is the original flight plan leg(s) and one or more offset reference points as computed by the navigation system. The computed offset reference point is located so that it lies on the intersection of lines drawn parallel to the host route at the desired offset distance and the line that bisects the track change angle. An exception to this occurs if there is a route discontinuity (or end of route). In this case, the offset reference point is located abeam of the original flight plan waypoint at the offset distance. The offset path and associated waypoint must be created to the same standards as the host route. The earth model must be WGS-84 and the offset reference point must have the same or better resolution than the host route waypoint. The parallel offset function shall be available for enroute TF and the geodesic portion of DF leg types at a minimum. Note: The parallel offset function enables an aircraft to be flown on a flight path offset from the center line of a route while maintaining all characteristics of that flightpath, as if it were being flown centrally on the route. Examples for the use of offsets are weather avoidance, air traffic conflict avoidance, etc. The system shall have the capability to fly parallel tracks at a selected offset distance. When executing a parallel offset, the navigation mode and all performance requirements of the original route in the active flight plan shall be applicable to the offset route. The system shall provide for entry of offset distance in increments of 1 nm, left or right of course. The system shall be capable of offsets of at least 20 nm. The fact that the system is operating in offset mode shall be clearly indicated to the flight crew. When in offset mode, the system shall provide reference parameters (e.g., cross-track deviation, distance-to-go, time-to-go) relative to the offset path and offset reference points.
