Not to forget sharing google documents and sharing google calendars, both of which I regularly do for work. Oh, and then there's the http://code.google.com/apis

Not to forget sharing google documents and sharing google calendars, both of which I regularly do for work. Oh, and then there's the http://code.google.com/apis/opensocial/ http://code.google.com/apis/opensocial/ api, designed by google as well.