Google Calendar has a new experimental feature in the works that allows you to check the availability status of people you're inviting to an event. In our early testing the experimental feature looks utterly broken, but once working it should be great.
If you'd like to see how it works, open any event on GCal and click the "sneak preview" link at the top of the event listing. This ability to view someone's busy/available status only works if they have a publicly viewable Google Calendar account, but many people do. Even as a work in progress, this is a reminder of how much room for innovation there is in online calendaring.
With the sneak preview turned on, the busy or available status of invitees to an event appears side by side with your own calendar, viewable as you drag a translucent box over possible times to suggest.
Right now it doesn't seem to work at all. Schedules aren't viewable until after someone's been invited to an event, the creator of the event is misattributed and a number of other problems have already come up.
It should just be a matter of time, though. If you're interested in hearing about the bleeding edge of calender innovation, check out Jon Udell's excellent interview this summer with Mike Douglass and Steven Lees, two men working on an XML standard for iCal. There is a whole lot of room for new developments in the world of online calendars, especially through cross-network standards that enable users of different systems to communicate.
We'd heard rumors about this new GCal feature for a few days but didn't confirm its existence until tech blogger Orli Yakuel Twittered about how to access it this morning.