Have you tried fixing your disk permissions? Some people were having Safari issues and this fixed it for them.DP4 is still crashing Safari tabs for me left and right. Also now other apps are crashing a lot (i.e. Sublime Text). So far I haven't noticed any improvements in stability from one DP to the next.
Speed is better though. Animations are better. And indexing hasn't been as bad.
Exchange support for one of my Exchange accounts is working better but not perfectly. The other account still is a mess (emails not syncing) but it has 60,000+ emails in the Inbox.