A good use for foursquare: Go to http://foursquare.com/feeds/ and copy the URL for the ICS feed. Now go to Google Calendar, find the “Other Calendars” box on the lower left corner and click the “Add” link on the bottom right corner of that box. Select “Add by URL” and paste in the Foursquare ICS URL. Now your Foursquare checkins show up in Google Calendar, reminding you where you’ve been and what you’ve done.