After many weeks of work, there is a post 9.0.2 Client Hotfix which should address the issues we've seen with Instant Search (In Outlook 2007 and Outlook 2010 not returning any results). If you remember many people were seeing that it was working, then it would stop, and then sometimes (days later) it would work again... then stop.
http://www.symantec.com/business/support/index?pag...
I've been using the fix for about a week now, on Outlook 2007 and Outlook 2010 (different computers of course) and I've got it in a repro environment which was previously broken, and it's all working nicely.
Once installed you need to rebuild the WDS Index on the workstation affected, and once that's rebuilt (which in my case took about 5 hours) it was all good.