How do you plan to use Google Calendar?
So, Google has started to incorporate Calendar elements into Gmail. The obvious Outlook-ish invitations work:

I love Google calendar, and have switched over, perhaps for ever. The integration with Google Maps is a killer, and the invitation system is boss:

I couldn’t get the supposed “auto recognition” of events to work reliably, although Philipp Lenssen at Google Blogoscoped makes it seem easy, unless I specifically used the phrase “can you join me for lunch Friday at 12pm” or the like. Invitations like “can you get on a telcon at 2pm Fri” didn’t work. For the moment, that is in beta, for real.
Note over on the left side, I have partitioned my world into a bunch of different calendars, which have different kinds of visibility. I make the Family calendar accessible to my family, but private to anyone else. I will be making the Conferences calendar public, so that anyone can see where I am — although I think I will rename to something like Stowe’s Whereabouts. My pal Greg gave me access to his calendar, and I will be doing that for him, since we work together a lot and basically have no secrets. Work, Work, Work is all the scheduled work stuff, like the endless telcons and meetings. My partitioning, though, I can click various things on and off independently. I would rather have tags, though, so that events could appear in multiple calendars.
So now my desktop calendar, iCalendar, is just a repository with subscriptions to the various calendars at Google. It have set it up to sync every hour, so when I am disconnected from the web I have a working copy. In this way, this model of calendaring is more like blogging than ever. I publish my calendar on the web (perhaps with protections), and I and others subscribe using a calendar feed reader — in this case iCalendar. And of course, iSync syncs the local copy at iCalendar to my phone (which Google doesn’t do, yet), which is just like putting a podcast onto my iPod from the RSS feed reader.