We're serving up static iCal feeds - Google Calendar etc can be configured to poll them for updates.

Here's an example of one of our public feeds (of Ruby on Rails events in Europe) - you can paste this in to the "Subscribe" menu in your calendar.

http://lanyrd.com/topics/ruby-on-rails/in/europe/ruby-on-rai...

You can see our subscribe UI in the right hand column on this page: http://lanyrd.com/topics/ruby-on-rails/in/europe/