After a few hours of using W7SE on my daughter's new netbook last night, I have no complaints. It's not very different from Vista, and Vista works great for me. Most of the features that are NOT included in W7SE are eye-candy and resource hogs anyway IMO.
W7SE does not include Windows Media Center, but it DOES include Windows Media Player, so no worries there. I never used Media Center for anything anyway. iTunes fills almost all of my media needs. W7SE does not allow DVD playback, but since we're talking about small netbooks that have no DVD drive, this seems to be a moot point.
To me, W7SE seems like a very good fit for small netbooks. As far as I can tell from what I've found online, W7SE is available ONLY as the OEM-installed OS on small netbooks, so using it anywhere else isn't even an option.
If I notice any interesting features or limitations from W7SE, I'll post them.