A while back I wrote a few blogs so I could get some detailed information out on how search folders work and how they can impact performance on exchange servers: Microsoft Exchange and search folders. I wrote it from the aspect on how it can cause 623 events which are JET_errVersionStoreOutOfMemory. One thing that I did not do was post any performance related information in the blog, however Mike Lagase is one of the performance guru's at Microsoft and works in my group. Being that many administrators are not verse in looking at performance monitor logs for these types of issue he wrote a fantastic blog. Please check it out: Search Folder Performance problem detection.