Xobni adds some extra features to Outlook, such as a sidebar featuring a search box, That search box allows you to search for an email according to any word in it or a contact.
It also creates statistics of the use of the progra and the emails: sent, read,... the number of messages sent by day and the time.
It can also extract phone numbers from the emails, a history log of the attached files and other that shows the chat conversations as if they were novels.
Personally, I have to say that it's one of the best plug-ins for Outlook you can find, it will save you time when finding a certain mail or contact. Xobni makes Outlook to be more efficient than ever.