If you're selected, Microsoft will supply you with the Tech Preview version of Office 2010 on a loaner laptop. You're expected to use it daily, and you might be tapped to tell your "real life story" about Office in an upcoming marketing campaign.
According to Microsoft's call for volunteers, they'll give you the loaner PC, 24/5 tech support, monthly webcasts filled with training and Q&As, and a free copy of Office 2010 when it eventually ships. The deal sounds kind of like Palm's earlier campaign in which they gave away a slew of free Palm Pre handsets in exchange for blogging. Sounds like a trend.
For all the details and the short volunteer form, check out Microsoft's Real Life Stories. Participants will be selected within a couple of weeks, so sign up fast.