1. Opening the Control Panel under Windows 7 takes about 2 seconds. Clicking an applet leaves you with a busy cursor for a second. These times aren't awful (my XP box takes about this long), but it's a notable contrast to the Mac, where the System Preferences is really fun and instantaneous. There seems to be a lot of "web-like" asynchronous UI in Vista and Win7, where you kinda get a frame, but then wait for it to fill in. These 1-2 second pauses make everything seem slow.
2. Windows 7 copied OS X's "keep this program in the dock" (they call it "pinning") very nicely. A migration from quick launch to this new thing would be nice, though. The mouseover screenshots that show you what's going on before you click don't seem to be implemented so well.
3. Being a long-time XP user, I still find the Vista/7 start menu confusing. Suppose you want to do start->run->notepad. You're actually "searching" for notepad, which rather than being instant, takes a second. But the result appears halfway across the screen from where you actually typed your search.
4. Libraries. Microsoft's brought back some of the Vista beta features and shows composite views of your Pictures, Music, Videos. Seems nicely done, but again asynchronous. For my collections it can take 5-10 seconds of waiting before I see content. During this time, the content pane fills up slowly, but mostly doesn't tell me it's working to find more stuff. I guess I don't want to replace synchronous folder views with 10 second async search views. Frustrating.
I'm impressed, as I've said, with Apple's Tiger to Leopard upgrade. Mail searches and Spotlight are now instant rather than taking a few seconds as before. Microsoft seems to be making some fixes speed-wise, but this core idea that it's okay to make me wait 1-5 seconds when I click, is really wrong. Seriously, this is why the web is winning, because Google cares about wringing out every 10ms.
I think it's a Steve Jobs quote: "How many people did you kill today?"
If Windows 7 and Vista waste 100 seconds a day, and there are a half-billion Windows users, that means 21 lives wasted per day.
Too many, I think.