I have used Yahoo calendar for years. Two reasons:
It will send me email reminders. This is an option I find really helpful.
Second, the sharing thing -- if you're in a Yahoo group that uses the calendar function, the dates on the group's calendar automatically come up on your calendar. This, to me, is another great function.
I have not yet checked to see if Google's calendar has these options.
So now Google Calendar is available at www.google.com/calendar You can manage your schedule and keep it private or share it with others...not sure that I want to share that much with others.
BUT - since GMail mobile, this is the first offering from Google that I like. I wasn't crazy about Google video and I thought the page creator was unnecessary.
But Google Calendar could actually be helpful! But I do wonder how comfortable everyone will be storing their personal appointments/meetings/rendezvous on Google's server.