There's a couple questions that I have myself in regards to AppleTV.
* will there be any problems wirelessly transmitting lossless music from mac to the AppleTV
* Will the quality of movies purchased be good or not? I have seen posts where the quality is bad. I have seen posts where people watch movies purchased through the iTunes store on their huge projector screens, and they look fine. Will you lose quality while it's wirelessly transmitting?
There's a couple of question there that keeps me scratching my chin.
Wireless shouldn't have an impact on the quality of the display. 802.11g peaks at 54Mbps, with a realistic transfer rate it about 20Mbps when streaming data. Movies and TV shows you get from iTunes tend to be about 1.2 to 1.5Mbps. Plenty of headroom for video. Lossess music is even easier to stream than video.
In my experience with a 40" Sony XBR2 (1080p display), iTunes downloads actually look better than what I expected when playing back via VGA on my MacBook. When they mean "near-DVD", they aren't lying. I have a few movies I ripped myself, as well as TV shows, and the quality is still quite watchable, far beyond Comcast's digital broadcasts.
But when you compare it to HD content, it still doesn't look "great". I have a couple HD rips that play back much better, but are nearly 4GB in size, and even then are only as good as Comcast HD, for example.