Interestingly, the trends Foursquare is following are particularly trendy among its closest peers. Facebook’s Graph API actually started off with OAuth 2.0 and has only ever used JSON as a data format. (Facebook even helped lead the creation of the new version, initially in the form of something called OAuth WRAP.) The smaller-but-still-scrappy location-based social service Gowalla also supports 0Auth 2.0 (though still has a basic authentication/API key system as well) and is JSON-only.

Foursquare, Gowalla and Facebook are an interesting trio to see converging. Since Facebook entered the location game they’re the three biggest players. Foursquare was the first to offer a writable API allowing third party apps to let users check-in to locations. Gowalla’s API got (official) write support only a few weeks before Facebook announced its location-based “Places” feature in August. Facebook provided a read-only API for Places to all but a few select partners from the feature’s launch until opening write access to all last month. Now Foursquare is the one playing catch-up, dropping XML support and joining its two competitors on the short list of services leading the industry in the move to OAuth 2.0.

The location-based social networking scene gets a lot of hype, but at least in terms of API competition and innovation it really is heating up. Just last week, Gowalla announced a major feature update, which it characterized as “the most significant update to the service we’ve ever released” on the company blog. Gowalla “now supports checking in on both Facebook Places and Foursquare” by linking a Gowalla account to a user’s corresponding accounts on the other services. The same APIs all three companies are racing to improve on various fronts allows Gowalla—which some might characterize as an also-ran at this point—to attempt a power-play by being first to admit its users probably want to access the other services too.

“Interestingly” indeed!