Not to beat a dead horse here, but the picture quality of projectors is so much worse than an LCD costing a fraction of the price that I would venture to say it is never worth getting one unless you are looking to set up a full high end (read: expensive) home theater.
Even with a high end, HD projector and a good screen, picture quality isn't always what you would expect. The room needs to be very dark (simply closing blinds/curtains is not necessarily enough), you will need to buy replacement bulbs, and the picture quality fades faster than with other forms of TVs and monitors. That said, if you do throw down the money for a good one, they can be really great if (and IMO, only if) you have lots of friends and family that would use it frequently in large groups.
I know it seems really cool to have a 110" screen and many of you may think it would be great to be able to play games on such a screen, but once you get over the initial "ooh and aah" factor, it is obvious you can do much better for much less. From personal experience I can tell you that in 98% of cases it is much more enjoyable to play games (and watch movies) on a 22" monitor than it is to do so on an HD projector.
