I tried it a while back and didn't like the performance so thought I would give it another go. If you haven't heard of it yet, here is a blurb from the site:
Xobni is the Outlook plug-in that saves you time finding email conversations, contacts and attachments.
After a quick install, you'll see the new Xobni toolbar appear in Outlook - and suddenly information will become much easier to find. When a new email arrives, the sender's full communication history appears in the Xobni sidebar, including past conversations, attachments and contact details. Xobni also includes a blazing fast email search tool.
So far it seems way better than before in terms of speed which was really the only problem I had with it. Let me know your experiences...