Yeah, the store has been incredibly slow since atleast 8.0, maybe before. It is quite frustrating since I work in the music field and I am constantly searching and buying music.
I have also noticed it takes longer to boot when you first start it up.
On my 2.0ghz iMac G5, iTunes 8.0 was actually faster software wise for starting up. On 8.1 it's about the same for startup time, but I get the spinning beachball for about a half a second every time I start it.
Scroll vertically.... I didn't know about this until now! It works a lot better to just move one or two albums apart, horizontal scroll seems to be more for moving to different parts of your library further apart. Maybe this update is Apple's way of telling us this. Horizontal scrolling is very inaccurate in 8.1.
I've found the update to be slower than 8.0, I'm seeing the beach ball a lot more often, although my uptime is now 18 days and I really need to see about upgrading from 1 to 4MB RAM...