Well you can spend $100 for an ATV or spend almost $1000 for a new TV, which you may not need, for the same(ish) features. And with the ATV, you can hook it up from TV to TV, bring it to a friend's place, or hook it up to a projector...
I recently bought a LG ST600 stream box for a cheap $50, and I can only assume a very similar interface is integrated into LG's higher-end TV's. Tried to stream some movies with it, and I hated it. YMMV, but I found the interface slow (like the remote wouldn't respond sometimes) and one of the biggest deal to me was I couldn't seem to fast forward or rewind in increments no less than 3 minutes! Kind of annoying. But that's LG, I would expect a bit better from something like Samsung.
I think it's best you decide what you would do with a stream box (Netflix, rent movies online, stream movies from your computer, sports channels which cost like $80/year for a subscription, etc) and get what you need. Try the stream/online features with the TV's at Best Buy, but it's not likely you'll be able to try streaming a movie from a computer or something.