I was using Xobni for a few months and really liked it, but wound up having to uninstall it a while back. With it installed, Outlook would hang upon launch about half the time. Once in a while, the whole plug-in (menu and side bar) would just disappear, and I'd have no idea how to get it back, and sometimes the search functionality would stop working. Hopefully it is (or is getting) more stable, because I really miss the functionality, and the plug-in I'm now using instead (X1) is horrendous.