The official Foursquare account just sent out a tweet letting everyone know that today is already the service’s biggest day ever. This is interesting since it’s actually the day before the SXSW conference kicks off in Austin, Texas. According to the tweet, Foursquare broke 275,000 check-ins (the previous record, set last Friday) for the day “hours ago.” This means they’re very likely well past 300,000 now and perhaps even higher

There are no shortage of location-based services launching this week at SXSW in Austin, Texas. Many of them allow you to “check-in” places to let others know you are there. So how do you differentiate between then and decide which to use

Back in November of last year, the location-based social event service Hot Potato launched at our Realtime CrunchUp. Today, they’ve taken what was a solid service , and made it a lot better with a number of upgrades. First and foremost, there is a new iPhone application that just went live in the App Store.

It’s getting tough to keep up with all of the location-related developments leading up to this year’s SXSW, and they just keep coming. Tonight, on the eve of the event, Plancast has just had its iPhone application approved. The service, which we’ve previously described as a ‘Foursquare for the future’, allows you to tell your friends where you’re planning to be as opposed to where you currently are (in other words, it lets you and your friends plan ahead).

This morning Google announced a new Blue Dot feature on the mobile version of Google Product Search that shows whether a product is in-stock at nearby stores. This seems to pose a threat to startup Milo , which highlights local inventory in product search results both on the web and mobile devices.

Apple has set the standard that once every year they will release a new version of the iPhone. It stands to reason that this year will be no different, with a new model likely coming sometime this summer.