The thing I'm by far the most excited about is AirPlay Mirroring. If I'm reading this correctly, I'll be able to mirror anything from my Mac to my TV using an Apple TV. This will be great for watching Internet videos, going through my iPhoto library with my wife, looking at home videos, etc. All without needing a stupid cable from my couch to my TV. The deeper iCloud integration is also intriguing. I assume this mean…
And that's the point the Apple TV goes from a hobby to a major product. Spending a £1000 on a Mac - I reckon another £100 for an Apple TV with that functionality as the hook is a pretty easy up sell.
Apps and/or Content deals with video distributors (Comcast/Verizon/etc) are going to be where it turns the corner. I suspect the whole hobby has been in a holding pattern while Apple has tried to line up the content deals and that the fallback plan is to just enable Apps and let the chips fall where they may. [1]
That's probably even the stick they'll use to get the cable companies to the table: Either they sign up and get preferential treatment in the interface, or they get shoved into being a dumb IP pipe that much faster.
[1] Delaying as the internals for an Apple-quality, app-running, 1080p set-top box get cheaper and cheaper hasn't hurt, I'm sure.