Forget Foursquare. Get over Gowalla. Jim Breyer of Accel Partners, a board member of Facebook and Walmart, is backing a different location-based app: Palo Alto-based Booyah, maker of an iPhone app called MyTown. Accel is leading a $20 million round in Booyah, and Breyer is joining its board — a ringing endorsement of the young company.

“We were super-stoked to have Jim join our board,” said Keith Lee, the CEO of the Palo Alto-based startup. “He understands retail, he understands digital media. And he understands it’s about the product at its core.”

The accolades go both ways. “Keith is simply a gifted and extraordinarily high-potential leader and entrepreneur,” said Breyer in an email. “[He] has passion, integrity, and is leading a company that sits at the intersection of media, social networks, gaming, and commerce. My gut tells me he is really going to pull something big off here.”

What’s Breyer so enthused about? Like Foursquare and Gowalla, Booyah’s MyTown app allows users to “check in” or announce their presence at real-world locations. But it mixes in more elements of game play and virtual goods, letting users “own” the digital versions of their real-world favorites and charge other users virtual rent, drawing comparisons to Monopoly. User numbers are rocketing, having quadrupled since January from 450,000 active users to more than 1.8 million. Foursquare, by contrast, took a year to reach 1 million users.

“We’re looking beyond the check-in,” said Lee. “Six to twelve months from now, no one’s going to own the check-in. It’s myopic to think that we’re battling over this check-in space. What’s going to be most important is how you create an experience that people are loyal to.”

Booyah had previously raised $4.5 million in 2008 from Kleiner Perkins Caufield & Byers’ specialized iFund, which backs iPhone-app developers. Kleiner and DAG Ventures are also joining the new investment round. Lee did not disclose the company’s valuation. But given that venture capitalists typically expect to take 15 to 20 percent of a company in exchange for the time commitment of a board seat, it’s possible the round valued Booyah at more than $100 million.

Accel’s investment is especially significant given rumors of talks between Facebook CEO Mark Zuckerberg and Foursquare CEO Dennis Crowley, as well as clear indications that Facebook plans to build location-based features into its social network. Since venture capitalists try to avoid conflicts in their portfolios, especially when agreeing to board seats, it seems significant that Breyer would choose to back Booyah even as Facebook’s location strategy takes shape.

Lee doesn’t see a conflict between Breyer’s role with Facebook and Booyah. “It only makes sense that we’d be working with Facebook and these larger guys,” he said. “It was much more about our connection with Accel and the mentorship they could bring.”