I use Vista on my Dell laptop since getting Linux to sleep and recover is still too spotty for my tastes but so far this is my experience with SP1:

• Started Install at 2:04 PM PST
• grind, grind grind
• Finished at 2:32 PM PST
• Process list reports dwm.exe (the 'window manager') is using ~27 megs rather than the 33 it was using previously
• Shutdown/Reboot time has diminished by around 5 seconds .. nothing to write home about as I don't reboot often anyway
• Switching between wired/wireless seems to pick up the networks faster and with less fiddling - previously Vista had trouble at times switching between the two and I would have to run their diagnostic tool to reset the ip
• There is a 'screen flash' present at login that was not previously apparent. Could just be a matter of waiting til everything settles down and might just need a defrag after all those files were updated
• Yep, O&O defrag reports the system went from 1.3% fragmented before the upgrade to about 8% fragmentation after

Overall, I don't 'feel' much of a difference. I copied a couple 1 gig isos across my network and the speed was fairly similar to what it was before - the calculation time was less, but the actual copy was almost the same but that could be due to other loads on this network right now (no, I'm not going to qualify that).

I cant say for certain but it looks like there might be one or two more services installed now that werent there before. Have to do a bit more research on that but contrary to what others have said this update does not appear to have re-enabled services that I previously had turned off such as windows search.

It will be interesting to see what other reports we get on this as it gets pushed out to the main stream users next month.