My first impressions of Google Calendar are very positive. I like the fact that they’ve already implemented data export (Atom feed or iCal format) instead of delivering it later or choosing lock-in. I’ve put a few events in there and have liked the feature set. One immediate specific use I see is as a podcast-scheduling service. As long as all parties have a GCal account, they can coordinate times and resources, and possibly even use GTalk to conference. Check it out.