I'm in Australia, so Netflix, Hulu and most that other stuff won't even work without proxying and other trickey. My net connection during peak hours is now massively oversubscribed so any streaming service is worthless until I get backhaul relief. OTOH I have 4TB of movies and tv shows in a range of formats, mostly MP4 but some MKV and I can't watch any of those without leaving on my expensive power hungry main machine with iTunes open. Streaming radio I can get through my amp, so I'm not concerned about that.
The AppleTV could be a really cool little device, everything is in place except for the parts Apple deliberately didn't give us, mostly I think to protect copyright holders.