There has been speculations for sometime now, that Google is developing a Calendar service likely to be called as gCalendar.
Another point supporting it is the case of gcalendar.com that was registered sometime back in 2004, owned by Data Docket Inc. which was affiliated with Google.
Now, there is a trusted tester program accessible through "http://calendar.google.com/tester". It points to the same place - that is not specifically for the calendar program, but as a general testing platform, that is generally developed by the companies for beta testing of the products, before they are launched into the market.
More Info on Google Trusted Tester Program is available at:
http://www.google.com/tester/faq
So, as I believe, and looking at the movements made by Google in the recent path, if Google Calendar is beta launched soon, it should not be received as an unexpected launch :)

