Outlook 2007 is a staple application on my desktop; it's always running, and I probably get more use out of it than Word on most days. But it's also suffered periodically from a kind of stodginess that seems to be totally unrelated to machine speed, fragmentation or anything else of the kind. Many people reported similar problems, and after gathering a good deal of user data Microsoft finally released a patch (validation needed) designed to address these problems, which they claim were due to contention issues in .PST access.
Thinking I could do no worse than I already was, I downloaded it and tried it out. The change was dramatic: Outlook now starts up markedly faster, and all operations with messages -- opening, moving, deleting, previewing -- are far speedier than they used to be. If you're running O2K7, go get it.
I also installed it and it's running great. No complaints. What I can say however is that when I goto delete an email it still takes forever!
[Make sure the Deleted Items folder has been emptied? --ed.]