If you haven't seen the ad here it is on you tube.
Here's a summary from CNET's Ina Fried:
In the ad, Seinfeld sizes up Gates' shoe size (a 10), asks him whether he's ever tried wearing his clothes in the shower ("never"), and ultimately asks Gates whether Microsoft is ever going to come out "with something moist and chewy like cake." Seinfeld asks Gates to give him a sign, like adjusting his shorts, if the answer is yes. Gates gives a wiggle in the affirmative.
Lets put that in context: here we have the emperor of Microsoft, a kind of Louis XVI in his own right, shrugging his butt in response to a question about letting the peasants eat cake.
Huh, are we sure the ad agency behind this is working for Microsoft?