No, it’s not official, but there are strong rumors that Google Calendar (code name CL2) will work with iCal as they use the same file format.
CL2 is closely, very closely, integrated with Gmail. It includes now-standard web 2.0 features – Ajax, suscription feeds for integration with iCal and other desktop calendars, event creation, search, sharing, notifications (including SMS) and more. – TechCrunch (with screen shots)
This is good news as I use iCal more and more every day. If I could sync iCal and Google Calendar I’d be great as I don’t have a WebDAV server to publish to currently.
Could be weeks before we get the official announcement from Google, but it sounds like Google Calendar will be a welcome addition to Gmail and iCal!