I am having the same issue at work and have done the patch recommended
on Brian's page as well as unplugging from the network. I did a test
on my 2.3 GHZ PC at home and my 3 GHZ at work and got very different
results.

Opening a 115mb file
Home 30 secs
Work 1 minute 15-45 seconds

It starts to open the file but the status bar pauses then Photoshop
shows as it is not responding... thus the application turns white for
about a minute and finally opens the document. I have just don't
understand why it would be so slower on what is a faster machine. I
have tried disabling the Symantec virus scan, but I am wondering what
else could cause photoshop to perform so poorly. I have tossed the
pref files by doing the ctrl + alt + shift... updating drives and
de-fragging... any other suggestions?