While doing more research on the rumored "Google Calendar", I came across some mentions of a "Trusted Tester" program accessible through calendar.google.com/tester. Knowing a little bit about how Google's web server works, I found that www.google.com/tester points to the same place -- this means it's probably not a "tester" program specifically for Google Calendar, it could be for all sorts of Google beta's.
And so I put on the rubber gloves and started digging once again. Logging in didn't do me any good as it's obviously for invited users only.
After spending a while trying to find anything that wasn't password protected, I stumbled across a FAQ for the Trusted Tester program that gives us some pretty interesting information. The FAQ tells us how Google releases products to a limited number of testers before they are given to the public. Google describes this program as the following:
The Trusted Tester Program gives the friends and family members of Google employees a chance to test early Google confidential betas and let us know what they think. To become a Trusted Tester, you first must be invited by a friend or family member who currently works at Google. You can then log on to the Trusted Tester website with a Google Account in order to access and test out betas of new Google products as they become available.
According to the FAQ, products are usually only released to this group for periods of about two weeks.
Google betas are usually only available for testing for around two weeks. After the testing period ends, we'll remove the link to the beta on the Trusted Tester website.
A program like this probably isn't much of a surprise to anyone -- most software development companies have a testing department of some kind. Google does it slightly different by extending this job to friends and family of its employees. This gives them fairly trustworthy circle of beta testers who aren't on the payroll.