I'm a bit of a Google fanboy, but I chekced out the Calendar and was nonplussed. I've been using Kiko (http://www.kiko.com/ for a while now, and it does everything Google Calendar currently does, in a nicer interface (at least in my opinion). iCal import and RSS subscription, flexible AJAX-y interface, etc. But the appointment creation interface is niftier to me: I can just write 'Fill out reports' and then add in catgories, locations, and contact invitations later as in the Google version, or I can write:
Fill Out Reports @Office +firstname.lastname@example.org [Work]
And Kiko knows what to do, creates my appointment and sets the Location as 'Office', the category as 'Work', and invites Bob via email, with no extra clciking or form filling on my end. Also, I can create an appointment and write 'Pay Phone Bill Every Month', or 'Call Accountant Every Week' and it does the Right Thing and creates automatically repeating appointments with no extra work on my part.
It can also send appointment reminders via email, IM (AOL only at this point), or even SMS, which is handy as heck when I'm out of the office. Calendar sharing with contacts or the poublic at large is dead easy too.
Plus, there's more features, such as syncing, coming. If you like Google Calendar, do yourself a favor and check out Kiko. It's free too and I, at least, like it a lot better right now. (And, no I don't work for them, but I have corresponded with a couple of the Kiko folks over email, and they are *very* responsive, quick, and nice, so I'm rooting for them. :)