You can now also comment on check-ins (above right), which should make the synchronization of schedules and meet-ups easier. To make the most of both photos and comments, there is now a History page on foursquare.com, which you can visit to see all of your previous check-ins -- including any photos and comments.
Foursquare has been working with its partners to make the most of the new functionality, too: Instagram and Foodspotting will both automatically create 'photo check-ins.'
For now, the only mobile Foursquare client for Android is picplz. WebOS is coming later this week, and BlackBerry in January. Developers will get access to the new API later this week.
Gallery: Foursquare App for iPhone