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Google Latitude, the search giant's mobile location service, has announced this morning that it is adding the ability to check in to specific places to its Android and iPhone apps. Android users will be able to check in automatically, using two brand new, different and very interesting methods. Latitude has now been live for 2 years and Google says it has 10 million monthly users, making it much more popular than the more high-profile startups in this space.

Why is Google working on mobile location tracking and sharing? It's all about search and relevance. "Our idea is to organize the world's information and part of that is location," Latitude's Ken Norton told us. "Location is a vector against which all factors and metrics will be considered."

Facebook launched Facebook Deals in Europe today, the location-based checkin service that offers specials and discounts to users who login and register their location using Facebook on their mobile phones. The service, already live in the U.S. since last fall, is now offering deals with several European-based companies as well as with some global brands, like Starbucks and Mazda.

Google Hotpot, the Yelp-like local recommendations service, has just introduced a new feature: filtered searches by friend. The way it works is this: when you search for a particular type of business on Hotpot, say "Italian restaurants," for example, you can click on a friend's name beside his recommendation in the search results to see all the Italian restaurants that friend has rated and reviewed, and see them plotted on a map.

The feature is also available now on Android phones, says Google.

The first in-depth user research study on the usage of the "Location" field within Twitter profiles has just been published by the Palo Alto Research Center (PARC). With a sample size of 32 million English language tweets in hand, PARC summer intern Brent Hecht selected a group of 10,000 active users to study. Remarkably, he found that 34% of Twitter users do not provide a valid geographic location on their Twitter user profiles. Instead, some of these users co-opt the field to make jokes, express their love for a particular celebrity or to shout back at Twitter that their location is "NON YA BUSINESS!" Others, meanwhile, provide no location information at all.

For any related service or other research study that leverages this field to determine Twitter users' actual location, the implication is obvious. Without first parsing the tweets to remove those that don't use the location field as intended, the sample data could be corrupted. PARC already found one study where that was the case.

Have you ever arrived at your local grocery store only to realize that you had left your trusted stash of carefully clipped and saved coupons at home? That may no longer be an issue with today's launch of geo-targeted mobile grocery coupons that work with mobile application Cellfire's network of 5,000 grocery stores here in the U.S.

Now, instead of browsing through the newspaper for coupons to clip, you can opt to receive a real-time alert on your mobile device of the coupons available to you, as you enter the grocery store itself.

"Location" was one of the buzzwords of 2010, but arguably some of the most interesting developments weren't how people checked in via Foursquare and the like. Rather, they were the ways in which people used mobile phones and mapping to report other things. The most notable example of this is crisis-mapping platform Ushahidi, which enables people to contribute reports during crisis situations either via SMS or the Internet. This real-time data is used for mapping and visualizations in the service of humanitarian response efforts. And to that end, Ushahidi has been described as "check-ins with a purpose."

According to Ushahidi, "check-in" - the sort of action more readily associated with location-based networking apps - via its platform has really been "only a metaphor." But that's changing now that Ushahidi is launching a new tool, Crowdmap:CI, that will make noting your location (and making location notes) easier.

Long a popular iPhone app for those looking for local recommendations, Yelp has finally released an app for the iPad. The app isn't simply a port of the iPhone features to the iPad, as it's designed to take full advantage of the larger screen.

You can, of course, still search for local businesses and view the results as a list or on a map. But the iPad app adds the option to view the results as a grid of photos. As the success of the food recommendation service Foodspotting has shown, photos - particularly at restaurants - can be a huge factor in making a decision on where to go, and by featuring the photos perhaps both users and businesses will feel more compelled to share more pictures on Yelp.

Location-based check in service Foursquare has just announced the addition of photos and commenting features, due to arrive within hours to users of its iPhone application. The features have already gone live on the Foursquare.com website.

According to Foursquare, these two features were among the most requested from its users for months, a signal that, perhaps, folks are beginning to demand more social elements from check-in apps: rewards, either virtual or tangible, are just not enough.

For those that have been busily searching Google's new Ngram Viewer to assess how language has changed over time, here's another project that might pique your interest, one that involves another great literary work, Roger Hargreaves's children's book Mr. Tickle.

The British Library wants to map different words and accents and chart the changing pronunciation of the English language. As part of its exhibit Evolving English, the British Library is adding to its already sizable collection of 20th century recordings of the English voice, and it's asking any English speaker worldwide to record their voice reading Mr. Tickle aloud.

Earlier this week, Twitter quietly announced new features for developers that make it easier to search for tweets according to location. The move, though not earth shattering in its own right, highlights the continual shift of Twitter away from being a communication tool to that of an information hub.

The announcement highlights a number of partnerships with location-based services like Gowalla, Localeze, OpenTable and TomTom, among others, that Twitter developer advocate Matt Harris says will "serve as a foundation for a number of exciting features we have planned to help users find what's new in their area and around the world."