I have to admit, I'm saving up for one of these:
http://www.sunshine16.com/TakeIt.html
I think I'd love it! I do have nerve issues in one of my legs and my back isn't the best either, thanks to being rear-ended too many times!! (I think I have a bullseye on the back of my car!) It hurts to stand and it hurts to sit too.
Luckily, I have a pretty good quilting set-up and I'm pretty good with quilting on my domestic. I just love doing it, and I can't imagine I'd love it on the frame as much, but I can see it being a lot faster.
Oh well! One of these days, I'll be able to take the time to do it! Oh! and I can only go to the fabric store on Saturdays and they never have a class on that day. And reserving the frame for that day might prove to be more difficult than it's worth!