Well, I must say that I work for Microsoft, so I've had access to early builds and time to experiment.
I've had several issues with lack of drivers too, especially because I have to run x64 edition for my work. What was worse, though, was that some of the available drivers were not reliable at all. One even fried my motherboard, as it would prevent my laptop from hibernating.
Speed - or lack thereof - is definitely an issue. I/O in particular seems to follow some crazy patterns, thanks to indexing, a/v, malware protection, superfetching and some pernicious tasks scheduled by our friendly IT dept.
Another bugbear of mine is the amazingly confusing number of versions we seem to have. I have even found an application that will work on enterprise but not on ultimate.
The good - if late - news is that those problems are being resolved. Driver stability has greatly improved, so has speed in my modest opinion. No, I have not got benchmark results, just my own usability impressions.
I have found some features I really like too

Here are some of them, in no particular order:
- The new UI: a definite improvement from Fisher-Price XP, even if it takes some time getting used to. I know, this is subjective.
- Symbolic links and extendable / shrinkable volumes: it may be the old Unix admin in me, but I like those
- Integrated search: a boon for disorganized or over-organized people like me
- The control panel: it now seems to be more logically organized. In particular, I like not having to fire up internet explorer in order to download updates.
- The security improvements. Yes, UAC is annoying - but it works. It must be improved, but the concept is good. So is the new re-architecting of service security levels.
- IE7: tabbed browsing at last
- The new TCP/IP stack: the performance is much better, especially in combination with server 2008.
- Modern hardware support: no more F6 - insert floppy (which floppy? who's got one of those left?). SATA, wireless and new tcp-offload-capable cards in particular. Video is still a pain point for some...
- the reliability and availability monitor: a nifty little utility to see where you're having problems.