I'm looking for some advice on whether to apply Exchange 5.5 SP3 to our servers that contain the mailbox stores for all of our employees. There seems to be a long list of problems with hot fixes listed on Microsoft's web site .
Service packs are a double-edged sword.
In general, I advise admins to test service packs on lab systems before installing them on production servers. This is especially valuable if your lab configuration closely matches that of your production boxes, since you can be more confident that your results will carry over outside the lab. In the specific case of SP3, unless you're worried about one of the issues in Q248838 or Q235452, go ahead and install it, but be sure to install the post-SP3 hotfixes, and be certain to run the Performance Optimizer after you do the install.