MSN Search is running the “MSN Search and Win” promotion for the month of February. The more you search, the more chances you might have to win. Check out the official rules.
How do you know if you win? From the rules:
When the Web Results of your Web Search are displayed, click the "MSN Search and Win" link located in the "Sponsored Sites" box on the Web Results page presented to determine if you are a winner.
I've done a few of the canned searches and saw the “you may have won” link; I've not seen it with my own searches, but I'll keep trying. Nonetheless, I've been impressed with the search relevance of MSN Search over the past few months and am quite happy using it.