I've been looking at calendar.google.com the past few days. One downside I see is that it is different from common web services that use REST.
The google calendar API uses Gdata, google's own protocol which takes a little getting use to so the stuff that I used at http://www.solutiongrove.com/mashup/ won't work.
Also there is a service package called Ajax Helper in OpenACS head that provides wrappers to Scriptaculous' javascript that allow developers to integrate effects and ajax.