I've been toying with the idea of getting AppleTV myself. Currently my PC is connected to my LCD TV via HDMI. I understand that when I get my new iMac I'd have to buy an adapter to get the same functionality. I see the adapter cable is actually a third of the price of Apple TV and Apple TV will give me much greater functionality as well as working with my iPhone 5 and iPad 3. As long as I can stream (mirror) large size 1080p MKV files I'm thinking Apple TV is the way to go. The ATV box will be just a few metres away from a new Airport Express which will be connected to a new i5 27" iMac.
Actually thinking about, it was useful to have the TV act as a 2nd screen, therefore one person could watch a movie whilst the other uses the PC as normal. I'm guessing I'll lose this function with AppleTV yeah?