Why do people 'check in' using Location-Based Social Networks? What is their motivation?

They're out and possibly bored with friends, and checking into foursquare is something to do / talk about. To show off their taste in restaurants and shopping places.

I honestly have no real justification for using foursquare, but I keep checking in places. It's almost a force of habit or a subconscious activity. I believe I may be trying to rationalize or recoup in some way the money I spend at a restaurant.

My initial rationale for using FourSquare was my terribly sensible wife — the pseudo-game mechanic would mean I'd remember to tell her when I'm at Waterloo on the way home. Now, it's partly that and partly the mild convenience of knowing Friend X who I've not seen in a while is round the corner and might be worth texting for a drink. And partly the Pokémon mechanic of mayoralties :)

I mainly use Foursquare, but also Gowalla, Yelp, TriOut and a few others. I do it for the reasons Ed mentioned - I like to be social. But there are benefits as well. So companies have figured out how to leverage the goodwill that is bestowed upon them by their check-ins. This is how a local BBQ restaurant hooked me for life by appealing to me via Twitter after finding me checking in. http://www.1918.com/social-media-case-study-how-the-pit-uses-twitter-and-foursquare/

I check in using Foursquare and have being doing for a full year.  At the end of 2010 it was useful to look back over the places I checked into especially cinemas. As an avid film goer when I was compiling my best films of the year I used my Google Calender as a reminder. However my Foursquare was more accurate.  So as a diary it works well.  I only share my checkins on Twitter when it is a cinema so checking in with FSQ buys me a tweet as well.  So all in all you appreciate the power of Foursquare after a years worth of checking in and taking the time to look back.  My film reviews are over at http://pip.posterous.com

In my case, I can think of two big reasons I check in: Become a topic of conversation and icebreaker for people that I enjoy socializing with in person, and to exchange good spots to check out with friends and contacts I admire and respect. Creates a situation where you might be pleasantly surprised to see a friend or acquaintance checking in at the same time, you have a chance to meet in person. This has happened many times for me. If your social lube is strong, these unexpected gatherings are usually a treat, one way or another.

Personally, largely three reasons: 1) personal record for various technical purposes, 2) personal record for nostalgic purposes (like taking photos), 3) as part of my personal digital footprint or lifestream, which also includes articles I'm reading, quotes from books I'm reading, ratings of books I'm reading, ratings of movies I'm watching. Though I suppose 3 is really just 1 & 2 extended.

People have different reasons for using Foursquare. Personally, I use it because it helps me keep track of where I've been. That kind of data in aggregate can be really interesting. It helps that Foursquare provides an iCal file that I can import to Google Calendar so that I can have a visual history of where I checked in and when.

At the end of the day, most people checkin because they are conditioned to do so. I'm unsure if much enters their consideration cycle after that. Similar question to 'why do we tweet xyz'. However, why did people begin? Early adopters try most things, just because. The game is addictive. Even if there is no tangible benefit, you may want to be mayor of your local cafe or keep a mayorship. To find deals at hotspots. I think reviews and tips is a segment that is growing.