I was just performing a search at Google and the line beneath the search box that typically says "New, Google desktop search....." had changed to be an offer to get a gmail account. When I followed the link it was indeed a genuine offer, and there was a notice that they are offering accounts randomly to Google users.
The invite posted on the search page reads:
New! Get Gmail - Google's free email service with 1 GB of space.
Forgive me if this has been reported but I could not find a reference anywhere on WebmasterWorld. I have a screenshot saved if anyone has an interest in the offer.