1) Foursquare was one of the most popular targets for DEFCON'S Wall of Sheep this year, next to Twitter. I believe the mayor of the con was also made the mayor of Sheeptown.
Interesting extension, but Chrome gives an ominous "This extension needs access to your data on all sites." I assume this is necessary to be able to read the targets of forms.
2) Their desktop site doesn't use SSL either, as my Unencrypted Password Warning Chrome extension (https://chrome.google.com/extensions/detail/mjpinemnkjlppmem...) will warn you, so it should come as no surprise that mobile doesn't.