I had these same problems when I upgraded to itunes... 7.1? I think it was... I tried going back to the previous itunes, but it didn't work (I did the whole copy everything, reinstall, etc but... can't remember why it didn't work, but it didn't). I hung in there til the next round of itunes came out with the fixes.
Backupbackupbackupbackup.
As an interim measure I'd make sure I'd restarted my laptop before I DJed (I tend to just close the lid and then open it again when I want to use the computer - I rarely close the whole thing down completely). I also found it really important to keep a certain amount of space clear (ie I didn't keep the laptop full as a goog), and to not use any app other than itunes when DJing.
All of this was way uncool, but it got me through - and I was DJing once a week for the month or so. Talk about freaking out while DJing. That beach ball is a bitch.
I'm sure there are fancier ways of coping with this, but I'm just a User, not a Support dood (that's what partners are for, right?).
....on a side note, I'm a big static person - giving a conference paper the other day I touched the track pad on my macbook to change a slide and delivered it such a massive static shock it froze the trackpad and the whole laptop shuddered and wouldn't move for a minute or so. There's nothing worse than standing in front of an international audience looking at a totally frozen computer and thinking "Did I just zap that thing with the electricity stored in my own body? I need to explore
other career options".