If you're seeing a lot of problems with Entourage's interaction with Exchange, you should open up a support case with your Microsoft account rep. We've got Entourage/Exchange tech support experts who can help you figure this out. Your users shouldn't have to empty their cache frequently. As you might guess, I'm an Exchange user too, and I have to empty the cache in any of my folders maybe a few times a year (and I'm running pre-pre-pre-alpha Entourage code, where we tolerate that kind of thing more!).
Also, since you mention that you're using Exchange 2007, if you're on SP1 RU4 or later, you might want to give the Entourage for Exchange Web Services beta a try. For more information about the beta, here's
the announcement of it on my blog, which includes some of the goodness that Entourage EWS brings you: faster Exchange performance, attachments in calendar events, sync of notes and tasks, and lots more.
Regards,
Nadyne.