Now first of all, Xobni is a great tool. I have been using it for a couple of months now. Its installs an Outlook add-in that makes search pretty quick inside of outlook itself and definitely better than the built-in default Windows search. Plus it has added social networking features and integration with Linkedin/Facebook etc which helps pull in contact information. While I have been a fan of Xobni for a while, there have been rumblings of discontent recently.
The first issue was when I found that I needed to split up my PST files (getting too large) due to the huge mail volumes here at ISB. Apparently in between, Xobni disabled the ability to search multiple PST files when they introduced a separate premium version. While older users were still allowed this, I had to go and reinstall my OS (moving to 7 RC), so lost out on this ability.
I finally moved back to my old tested and tried free desktop search tool, Copernic. I enabled only email search for the tool. While I may not have it available as an add-in, its still pretty comprehensive and accurate enough.
The fun actually started once I uninstalled Xobni today. Outlook suddenly became much much more responsive. Folders opened like that! I just realised that my Outlook had become so slow over the past few months, but I had just gotten so used to it that I stopped noticing it!
So if you have it installed. Try removing it once and see the difference. Trust me, you dont want to go back to it, advantages or no advantages. Oh, and give Copernic a whirl. Its an excellent search engine for files/mail etc on the desktop. I find it better than windows and Google desktop search as well.