Rear projection is tougher off-axis and has the long term cost of replacement lamps that may be necessary. There also is the concern of the moving parts or burnt panels within any projection technology - but not enough of a worry that I would consider it major. RPTV (new digital formats, not CRT) don't suffer from burn in and give you a sharp image which is plenty bright enough in most rooms. Great for gaming or general TV viewing. Plus, you can get very large sizes without jumping a ton in money, though, IMO, smaller sizes tend to be far more than they should be.
Flat panel displays (FPDs) still take up far less room, they really are designed to incorporate into your room seamlessly. When combined with in-wall or on-wall speakers and IR repeaters they become as much a lifestyle statement as they are a piece of A/V gear. They tend to be very good from any angle - plasmas especially - and can be turned on/off very quickly instead of having warm up times or cool down periods. No replacement lamps... and they tend to last 20+ years with normal usage.
But, plasma, if you aren't somewhat cautious, can suffer from burn-in which is at least a bit of a concern if you play a lot of video games and aren't aware of the potential. Flat LCDs do NOT suffer from burn-in but some consider their pixel refresh speed to be a bit slow which can cause some blurring with faster action.
Most of all, as sizes get larger and larger, prices tend to get very high on these products, very quickly. This year we are finally seeing 50" panels drop below $3,000... But, 60" models are still very pricey.
Finally, neither technology is as solid as the old style CRT displays. Color and black levels from CRT simply are the gold standard that have not been met by any of the new digital technologies... yet. SED panels which may be out late this year... maybe... are rumoured to be much closer to CRT in image quality, but similar to a plasma in design. Hang it on the wall - have a great image.
Personally? I've gone with plasma for my displays right now along with front projection. Plasma is just great for day-to-day viewing and being able to hang it on the wall above a dresser or behing a electric screen makes it blend well into my home environment. The rooms where it doesn't matter as much I hang some old CRTs from the ceiling.
