Facebook, Foursquare, and Gowalla (along with several other companies) now have a little more competition when it comes to location-based check-in services.  Starting this afternoon, Google Latitude users can also let their friends know when they’ve arrived at a certain place.

Google’s rationale for this upgrade is that check-ins add context.  Now, rather than just seeing a pal is on a certain street, a user can figure out whether he’s grabbing a drink at a coffee shop or buying a new vehicle at the adjacent car dealer.

As for how it works, the check-in process can be about as discreet or obtrusive as desired.  Options range from notifications – where Latitude will nudge users to check in at nearby places – to automatic check-ins and check-outs to keep people from fumbling with their phones or appearing to spend the night at Walmart.

Then here’s an incentive for individuals to play along: the act of checking in can take a person to a business’s Place page, allowing them to learn more about it.

There shouldn’t be much to worry about on the privacy side of things, either.  A post on the Official Google Blog explained, "[W]e thought carefully about how to make checking in to places quick and easy while giving you control over your privacy.  Just like when sharing your location with Latitude, checking in is 100% opt-in, and you can choose to share any check-in with your friends on Latitude, publicly on the web and your Google profile, or just yourself."

The main problem, of course, is that Google’s quite late to the check-in game and could have some trouble getting potential users’ attention.