Geekdad linked to this -- My Mini City. It's a Simcity-ish Flash game where the population of your city grows based on how many visitors you get to your specific URL. I don't have one, but you can click through to boost Geekdad's population or use a different URL to boost his industry so his sims have jobs. It looks like later you get URLs for other tasks like transportation, security, environment, business.
This just begs for a Facebook app doesn't it? There are several Facebook groups where people are trying to get clicks to build their city bigger but no application.
It's kind of an interesting model. It's sort of pay-per-click, but it doesn't cost Motion-Twin (the company behind it) any hard cash to get clicks. It's just a virtual reward except for the cost of serving up the site and the Flash file(s).
What surprises me is that they're not monetizing their traffic except for their own ads for their own games, which as far as I can tell are free. The top 10 cities have over 10,000 residents. The stats for the US alone shows 14 million inhabitants in 478,615 cities over 36 days. That should translate to at least 14 million visits. That probably translates to well over a million unique visitors if 478 thousand signed up.
If someone like John Chow were to monetize that amount of traffic, he could theoretically turn a million unique visitors into $250,000 in a month. That's pretty theoretical, since John's the master monetizer and someone clicking through to a free Flash game probably isn't about to spend as much as a visitor to John's blog. But it could be even easier if you just ran a few ads for casual games like Bejeweled. But if you could do a tenth as well as him, that's $25,000 a month. Not bad for a pretty simple Flash game and webapp.