I haven't committed just yet, but I am eventually going to buy an ATV. Right now I have my computer plugged into my TV through HDMI so I just dual monitor my system and play my iTunes movies on the plasma.
My big thing right now is deciding what my future movie library will look like format wise. I have an xBox 360 and so stream NetFlix through the included application, and I am pretty set against going to BluRay. So for now if I want an HD option for movies I have to look at DLC options. Apple seems to have the best selection so far, and the best infrastructure for delivery to the TV.
I know BluRay is all the rage right now, but 1.) I dont see hard copy formats sticking around too much longer, or at least they will be (and indeed already are) rivaled by DLC options. 2.) I hate Sony (for stupid reasons, but its still a factor) 3.) I can buy a 1TB external HDD for my computer and carry nearly every movie I will ever own with me, where ever I move to. Sure I cant let people borrow them, and thats certainly a drawback.
I haven't committed yet, still looking at all the options, but I think within the next year or so I'll pull the trigger. Probably after the next ATV refresh.