Several users have asked how to use Spanning Sync to sync iCal with multiple Google accounts, for instance a work-related account and a personal account. Here's how:
Let's say you're syncing iCal to your personal Google Calendar account and want to add calendars from your Work account. First you need to share the calendars from your work account with your personal Google account. To do this, log into Google Calendar (using your work account), select "Settings", then "Calendars", then "Share this calendar" for each calendar you want to share. Under "Add a new person", add the email address associated with your personal Google account and select "Make changes to events" for the permissions.
Once you've done that, you can to log into Google Calendar using your personal account and see both your work and personal calendars. Now refresh Spanning Sync by quitting System Preferences and reopening the Spanning Sync preference pane. You'll see both your work and personal Google calendars listed and be able to sync with all of them.
Note that this works with both traditional Google Accounts and Google Apps for Your Domain accounts.