The only problem we had going from VSE 8.7 to 8.8 was Outlook's extend.dat, which is stored in
%userprofile%\Local Settings\Application Data\Microsoft\Outlook\extend.dat
The thing that totally bit us in the kiester with 8.7 to 8.8p2 wrt to Outlook 2010 was this gem:
Outlook 2010 stops responding or has performance issues after VSE 8.8 mail scan plug-in is loaded
Until p4 gets released at least, you'll probably want to disable on-deliver scanning of email unless you want to frustrate users with very intermittent, very hard to debug, might infuriate C level executives pauses in Outlook that hang the mailbox for 10-50 seconds when it happens. You'll probably get smatterings of regular user complaints that aren't actionable, frequent enough, or indicative of VSE enough until someone important enough says that it's driving them entirely bonkers, and them someone stumbles on some discussion threads like these after googling "outlook 2010 hang mcafee" on a hunch that Mcafee is probably involved somehow.
It took us a few months to get a bead on it. Once we disabled on delivery scanning in 8.8, the problem evaporated.
At least I'm not bitter. :-)
Product management: please get p4 released? Pretty please?
(this issue was in addition to fighting against 8.7's access protection and an apprent bug in ePO and 4.8 agent wherein older 4.0 agents would apparently not take the "disable access protection" policy directives on an epo 4.6.6... which made installing an upgraded agent and/or VSE 8.8 next to impossible on older agents in a 4.6.6 ePO environment. Upgrading agent 4.0 to 4.5 on the way to 4.8 appeared to work around all that fun).