I have a Google account, so here's what I did:

• Subscribed to my calendar in OS X iCal. This gave me two calendars: my local calendar, and my Google calendar
• (optional) Moved all of my local calendar entries onto my Google calendar, then deleted my local calendar (this ended up making my Google calendar the default, and got rid of the local calendar so I wouldn't accidentally use it).

  Now all of my calendar entries are created on Google by default.

• Set up Address Book syncing with Google in Address Book prefs. (Preferences/Synchronize with Google)
• Repeated all of this on each machine you want to sync to your Google data. You can include an iPhone in the mix too by syncing Google as an Exchange server.

One caveat: I did lose some entries one time where I guess iSync screwed up -- entered them on one Mac, and they vanished next time I synced.