Gmail was released on April 1st, 2004. I’ve heard talk that Google Calendar will be released on April 1st, 2006. None of those sources have any credibility though. The only source that has any kind of reliability is Valleywag, (they predicted Google Page Creator) but they haven’t said anything about Google Calendar’s release date.
When Google Calendar finally does come out, I expect it to have almost every feature that Outlook’s calendar has, or an improvement on those features. Right now, I use 30boxes.com for my online calendar, and its interface just doesn’t cut it. It’s nice because it’s built with AJAX, and it has tons of features, but the scrolling on it is terrible. You have to click an up or down button and wait for the next week to load up. It doesn’t take long, but that kind of thing should be prefetched in the same way that a Google Map prefetches offscreen areas of the map. 30boxes’ scrolling mechanism is just like Yahoo! Maps’ scrolling mechanism. It’s the old way of doing things.
You can count on Google Calendar implementing it the same way they implemented Google Maps.