Many are experiencing problems with Entourage beachballing and pausing. MacWindows has a solution below that has worked very well for me. Far less disk activity and better performance, not just in Entourage, but overall.
News Update, May 5
Spotlight cripples Entourage in Tiger: a fix is offered. May 5, 2005 -- Several readers verified the problem of Entourage in Tiger getting stuck in "spinning beach ball" mode, which we reported on Tuesday.
Joe Selvaggi blames it on Spotlight and has a suggestion:
I am experiencing the spinning ball problem in Entourage since upgrading to Tiger. There a corresponding sound (like frantic memory/ disk swapping activity) coming from my PowerBook. Apparently it's Spotlight trying to index the Entourage Mail DB. Tell Spotlight to ignore the Microsoft User Data folder (Users > Documents > Microsoft User Data) should do the trick, or at least it appears to work.
MacWindows