Foursquare vs. Gowalla

There are some impressive numbers in the analysis below:

• Foursquare Is Five Times Larger Than Gowalla And Growing 75 Percent Faster Every Day

Here's an analysis from back in June which provides a differentiating (ok, somewhat obvious) insight – Foursquare better integrates with social networks:

• Checking In on Location-based Services: Foursquare vs. Gowalla vs. Brightkite

Do you use one of these services? Why? What makes it a compelling experience for you?