I’ve been using the Xobni outlook plug-in for the past couple of weeks. And I love it. A few of the features don’t really work for me (Skype out, mobile number displayed rather than work), but:

• the search feels as fast as LookOut
• threaded conversations are the way email is meant to be read
• attachment discovery adds valuable context about your interaction with a correspondent

And the price is right (for now). If your professional world lives in Outlook, then you need to try Xobni.