I tried it out on my laptop - a Dell Inspiron 600m with a 1.2ghz celeron and 1gb RAM, and doesnt support aero. It's very netbookish in specs. Results were not so good. It was pretty slow, even as compared to Vista IMO. And the sound drivers fail to work properly, which is rather odd as earlier Win7 betas worked just fine with the audio in this laptop. Audio problems aside, normally I'd say those specs are pushing it, but they are claiming that Win 7 is going to run well on netbooks. Based on my experience, they better have some sort of special netbook version thats stripped, because performance was just not there as compared to XP or Vista. But it's a beta, of course. 😛
I'm waiting for the x64 before I give it a go on my main desktop, and I'm really excited to use it on my new HTPC when the parts arrive. The updated media center is fantastic IMO, best HTPC software I've used to date. It was so much easier and smoother to use than the vista version.
Aside from performance issues though, I have to say the new libraries feature is probably my favorite of all. I have most of my content on a server, and I have to configure all of my clients to point to this music folder, this docs folder, and then in order to keep things updated, manually save to the server folder, etc. In Win 7, I just add that server music folder to the music library, set it as default, and remove all the others. As far as that PC is concerned, the only place for music is that server share, but thats completely invisible. Makes management so much easier, especially for multiple users - they dont need to find their docs or photos folder on the server, just go to the docs library when theyre logged in. Brilliant.
The real magic happens when programs are preconfigured to use those libraries. I just fired up media center, and it started filling in the music library. No need to point at the server share specifically, it obviously knew where to look. And if you've ever used Vista media center, you'd understand how traumatic an experience it was to just get it to monitor a single folder and only that folder. Its SO much easier to use now with the libraries.
Other niceties with the media center was some actual text in the video library, so you could actually find what youre looking for amidst the thumbnails. The progress bar is now clickable (finally!). And it can play xvid all on its own. The main menu is still a little cluttered and not configurable enough (I *really* dont want the sports tab), but it's *much* better than before.