I want to thank Skidpad and the other contributors to this thread, and add my similar experience.
We had a 32" Samsung in a niche created by a prior owner. The niche had been wired with coax, L/R RCA for audio, and RCA composit component wiring, all wired to the right corner of the room where a media center was located.Attachment 154329Attachment 154330
I went to Magnolia AV (Bellevue, WA), and they helped me realize first (before I found this thread) that I could cover the niche with a 54" Panasonic plasma (TC-P54G10). Like a prior thread here, it was first suggested that I use a mount to the back of the niche as was suggested to an earlier poster. But then I saw Skidpad's post and suggested we do something similar.
We needed to account for the fact that the studs were at the front and back corners of the niche, so the sides of the "H" strut covered the sides of the niche.
I wanted to be able to tilt the screen L-R and up-down, so I sprang for the Sanus VisionMount VMDD26, $600.Attachment 154331Attachment 154332
Magnolia charged me $750 for delivery, buildout and setup, and they were very professional.
The only thing I would make sure you consider if you want to cover the whole niche and you are cutting it close is that the niche may be visible from other perspectives of the room, and depending on how it is tilted
I would do Magnolia again--they did a good install, and the prices were the same as BestBuy or better: $600 for the bracket, $750 for the install & delivery, $1700 for the TV, plus $200 off a $250 Panasonic Bluray player (DMP-BD60K) and $300 off a $650 Martin Logan Dynamo subwoofer.