Clever, or Disconcerting?
Clever? Probably not. It’s a medium-tech trick used better in a few other specialized sites, and it reveals less (to them, the advertisers) than it appears. I’ve seen it done in print too, like in catalogues mailed at Christmas with my name emblazoned on a gift item inside. It bothers me a little when it’s done for the purpose of advertising this way though – It seems so… cheap.
And it sure does look like some sort of spying (and privacy invasion), doesn’t it? If they haven’t already, these ads should disabuse you of the notion that you have anonymity online. You don’t.