I talked to the Y-Cal folks late yesterday afternoon (turns out they are just down the hall from me). The word is: there is an API for Y-Calendar and it will be released this year, but they are not at liberty to say when. (The Project Manager is still sorting out the features-lists, I gather.) For the time-being take a look at the Y-Upcoming calendar and see if you can craft some code using that API. Once I get the official announcement, I'll put something up in the Perl section of the Yahoo Developer Network.