Here's an interesting concept that circumvents some of the challenges of integrating advertising in online maps. SEW points out that the rooftop ads probably aren't for the sake of online mapping satellite imagery; they actually target commercial flights as they approach airports.
It still makes one wonder about the possibilities in online mapping. It probably wouldn't take off to a large degree; and if it did, mapping providers would likely blur out any ads that didn't pay for placement. But it's an interesting anecdote that demonstrates the creativity of marketers finding every last nook and cranny of advertising space in the physical and online worlds.