I strictly used a 106" display for several years. The only reason I went to a plasma was because the ambient light in the room was killing the TV experience completely. You do give up a TON when watching SDTV, but you also get used to it, and expect the loss in quality. Not a big deal really once you are used to it and accept that SDTV is truly flawed. Yet, you do start looking very intensively for HD shows that you enjoy. A lousy HD news show is far better than a good SDTV version.
After moving into a home with to much light for full time projection use, we got a cheap 50" plasma. It was something we used for a couple of years, but then went up to a 60" Pioneer plasma. No doubt, we enjoy the Pioneer immensely, and it's a better display, by a long shot, compared to the projector. But, the projector truly immerses me in the video in a way that the 60" plasma could only dream of doing.
I'm a huge fan of using both, but only because of lamp life, which is of some concern with how much the TV is on in our home, and because of the ambient light. If we had a far darker family room, like our old house, I have no doubt we would use the projector exclusively at this point.