It is a most worthwhile cause but my experience from a few years ago leads me to keep well clear of the organisation because of poor organisation and uncertainty right up to the day you should be taking "passengers"
It may be very different now, I certainly hope so.
What kind of issues were there?
From what I hear, one important thing is to have a plane which "older" people can get in and out of easily, which rules out quite a few types.
My experience of doing Project Propeller was very good. I think it's wise to contact your assigned passengers in advance to make direct contact and the necessary logistic arrangements.
As Peter said, getting them in to and out of the aircraft can be quite tricky. I had a C182 which is generally considered pretty easy since you don't have to step down in to it, but we still struggled a bit with one chap. Frankly though, the whole thing was so rewarding I think it's worth almost any amount of hassle.
It is an inspiring day and you are expected to be active in the organisation. I've already made arrangements with one vet and have an open door for a second that the PP team will use if they wish and they'll give me and the vet each others contact details after which it's up to us.
The whole thing depends on volunteers and everyone mucking in and therein lies much of its charm
I shall be doing PP again this year, it has been a wonderful way to get to know some really interesting old RAF veterans, two of whom I now regard as old friends!
I've done it once, and found it incredibly rewarding. I hope to do it again this year. Given the challenge, I thought that the organisation was pretty reasonable, although there was the odd minor communication glitch.
What kinds of planes did you people do it in?
I know of one bloke who turned up in a twin and got bogged down and they had to pull it out with a vehicle.
I did it in an Arrow III (which was a bit of a phaff, getting the arthritic pax in and out of, due to only one door), a Cherokee 6 and my current Saratoga.
It really is a terrific day out with some amazing veterans who, to a man, were interesting, funny and self-effacing.
One chap that I had in 2009 (a Lancaster pilot) recounted the tale of a sortie over occupied territory where they had encountered heavy airframe icing; unbeknownst to them, one of the 500lb bombs failed to release over the target and remained hung up in the bomb-bay until they descended back towards their base in east Anglia, and dropped below the freezing level. "We came within an ace of bombing Ely cathedral", he mused...