Lower quality, in general (primary due to light reflecting off dust, in the proximate atmosphere), other objects can also interfere with the projection, people walking across and whatnot, so this effects placement. The best place to have them is on the ceiling, usually. Image takes the attributes of it's surface, which isn't an issue if you have one of them board thingies, they don't have any built in sound that I know of so you will need a set of speakers to output sound.
Generally though the image looks lesser in quality, over all. With reduces colour fidelity, and looking slightly more washed out, but still great if you have a good place to set it up, and a good projector. Honestly if you can get a setup like that isn't intrusive, it's probably the best way to go. (like if you want a gaming (exclusive) room).
By the way, I just noticed your name. If you're intending to do it to a Wii. Do not, stretching the image out like that will make it look real garbage.
