Not long after Foursquare founder Dennis Crowley told me the service has signed up 300,000 businesses (and 10 million users), business development lead Eric Friedman blogged today that it has reached 500,000.

To be clear, Foursquare is not yet monetizing these businesses but rather letting them sign up and manage various check-in deals and specials. But it still shows a great deal of momentum.

Also, because the biggest barrier to entry is self provisioning (vs. cost), this bodes well for the day when it flips the monetization switch. In addition, it will increasingly work with local resellers, as GM Evan Cohen told us at ILM East.

Currently, it’s “evenly divided” between SMBs and larger chains that are geographically distributed, says Cohen. Check-in deals and LBS promotions aside, it has also done lots of brand advertising such as sponsored badges.

This will continue to evolve quickly as Foursquare’s growing team is iterating and churning out new features faster than ever. We’ll get to hear a lot more from Tristan Walker at our Deals 3D conference in two weeks.