Can't help feeling that many of the problems noted above are due to unrealistic expectations. If you want, for example, to stream non iTunes stuff get a WDTV Live this device does exactly what Apple said it would do, I bought it on that expectation and I am thrilled with it.
First off - sure, if you buy this and expect not to have to use iTunes, that's pretty stupid. I have no doubt a cloud or even NAS-based system will be on the way at some point, but right now it's very obvious you need Home Sharing and whatnot enabled to use it.
(As an aside - I'm certain Time Capsule or APBS could be updated to support some manner of home sharing without needing a computer turned on all the time, perhaps only needing to authenticate when you're copying stuff to it?)
I think the complaint is more of a UI issue than anything, going by the comments. You've now got a bunch of extra clicks to get to iTunes streamed stuff.
I was about to pick one up when I realised they've relegated all your existing content into one corner under 'Computers', and put the (practically useless in Australia) rental stuff front-and-centre. This is not only for your handbraked/torrented/etc DVD's and TV Shows, but stuff you buy via iTunes on a Mac as well.
It strikes me as odd when the very point of Home Sharing and whatnot is to essentially create a unified home library of all your content that can be accessed by a bunch of different devices. The current distinction on Apple TV doesn't really sell that concept at all.
It's doubly weird because Take 2 fixed this particular issue with the old model ('My Movies', 'My TV Shows', etc). They've regressed the UI.