a new revenue stream, sweet. To bad Facebook and Bing are winning the web away.
Microsoft Ad center was also a walk in the park compared to Google Adsense. I am a novice though.
Obviously at this point it is largely just offsetting personal email, but I don't think it's reasonable to dismiss that as insignificant.
you do have to consider many of those searches as looking for stuff already in their social graph (friends, pages, etc). i know i use their search to navigate all the time.
The new layer is data locked into private site that farm content.