I was, until a few months ago, firmly decided on a plasma (50 inch) to replace/upgrade my current 32 inch SD CRT. A good friend of mine got one and I helped him set it up and tweak it. However, largely by accident, I got to play around with a business projector (now two different ones--LCD and DLP) from my wife's office and I was able to generate a 65 inch image (room constraints prevent any more than that for now), which is significantly bigger still over my 32 inch TV. I even played around with the pj to make a 50 inch image, just to compare. There is no comparison, to me. Bigger is better. And so I've decided to buy a projector instead of a plasma. True, my projector will only be 720p, but then, the only plasmas I was in the market for are 768p--not a significant difference. And I will save A LOT of money (my DIY screen has cost me nothing so far, and will come in well under 100$ all told).
For the price of the projector I'm getting, the largest plasma I could buy (on my side of the border) is 42 inches. At 50 inches, the cost is double my projector. At 65 inches (63 being the closest one I've ever found in plasma), the cost is FIVE times the amount. At 70 inches...well, you get the idea.
Plasma PQ can probably be better than my PJ, but the size factor trumps the difference to me (it helps that I'm not nearly as fussy about video as I am about audio, admittedly). I suspect that when my TVs need replacing because they don't work anymore, either a plasma or an LCD flat panel will replace them--I only have room for ONE HT in the house.
But, for now, I've chosen the projector route and I'm quite happy (especially when I consider how much earlier I can get into HD DVD/Blu-Ray with the savings).