We bought one so that our Mac Mini could go back to being used as a computer rather than a movie player. It's much more limited in what it does than the first generation, but then it's tiny, consumes virtually zero power and is completely silent and plays nicely with our phones (Airplay).
You can use iTunes home sharing to play content from your iTunes, bit of a pita because the account has to be logged in and iTunes running in order to be visible to the Apple TV, the sharing is probably the weakest part.
They need to do a deal with the BBC and bring iPlayer to it, then it'd be a much more attractive offering for the UK. Still, if they do open it to app developers then we should see a native BBC iPlayer client as the BBC are already working on a native client for other iOS devices, wouldn't hold my breath for this as it's still regarded as a "hobby" to Apple, they've obviously got grand designs on some future product and are iteratively trying things out.