I've been using the google calendar for quite a while. I just stumbled across a blog posting describing how to load a couple of Thunderbird plugins to connect Thunderbird to my google calendar.
The blog posting, http://bfish.xaedalus.net/?p=239 , works fine - but expect some oddness as this is all early release stuff.
I haven't looked at the Sakai Schedule / Calendar tool, but a Lightning Provider for Sakai would be sweet.
More information on Lightning can be found at the Mozilla Wiki's Calendar area.