If you've recently created an event in Google Calendar, you may have been asked to take part in a "Sneak Preview" of a new event interface. You probably should, as it could save you from reading lots of clarifying emails.
Basically, the new interface grabs the public calendars, or private calendars shared with you, of any people you're inviting and mashes them together in a mini-calendar under your event interface. You'll see everyone's schedule for the day or time span you're creating an event for, and can move your event around physically in between everyone's appointments. It adds a nice Outlook-like capability to GCal, though for events with invitees who aren't that into web calendars or public sharing, contact-and-ask services like When Is Good, Doodle and TimeBridge will continue to be useful.
Google Calendar Sneak Preview [Google Operating System]