I've been pondering this myself. Initially, I wanted an AppleTV, but as time goes on, I'm not so sure. They seem rather nifty and a great idea, but I can't help asking myself "why?".
I have something on the order of 250Gb of movies and well over 500Gb of TV shows ripped for playing on my iPod. Now without having to double rip files I don't see a real advantage of the AppleTV over an iPod. At this point, pretty much everything coming out of iTunes is still iPod compatible, so the iPod is the lowest common denominator and the default format. Why do I want to buy another device to watch my movies when they are already in the iPod format with varying degrees of rip quality? I can simply plug in my iPod and watch them on my TV from there.
I'm still pondering this, but I'm not seeing myself willing to double rip my library or fork out for another device, not yet at least.