Aero, WDM, keeping the user in user mode instead of by default putting them in admin mode. A lot if it is under the hood and was actually implemented in Vista. Also, I really do suggest giving the 7 interface sometime - the new taskbar's management of your applications (running and not running) is really superior to Vista and before - they borrowed a lot conceptually from the much acclaimed OSX dock, but maintained what kept the original Windows taskbar present for so long. From the HTPC end, I know this is perhaps taboo to say on these message boards, but WMC is really great - Microsoft frankly hit it out of the park there. Everything just works and I don't have to worry about it.
As far as servers go, I suppose a little more specificity would be required there - what kind of server? Is it a headless server? A media server?
As for file-sharing, the normal file-sharing works as well as it did in Vista, as in I don't have any of the problems as I had in XP sharing files (network shares sometimes working/sometimes not working, file transfers quitting mid way).