Now you have got your Google Calendar Sync running, but chances are that you have set up multiple calendars. You will notice that the default sync does NOT include additional but only the main calendar.
I am using the main calendar for scheduling everyday appointments and a second one for recommended TV shows (I have set up the open source TV-Browser to automatically add TV favourites to my Google Calendar, but that is another story).
Here is the solution for your "I want to sync multiple Google Calendars with my iOS device" problem:
What you will need:
Firefox Browser 
User Agent Switcher add-on
NoScript add-on
Assuming that you have set up Firefox and the add-ons do the following steps:
- change your Firefox user agent to "Mobile Safari 3.1.3 - iPhone" or equivalent using the User Agent Switcher add-on
- browse to m.google.com/sync
- change the language to English (at the bottom)
- disable google.com JavaScript for the google.com domain using the NoScript add-on
- choose your device and set up the calendars to be synced
If your iPhone/iPod Touch/iPad is not listed under devices in the Google Sync options visit https://www.google.com/calendar/iphoneselect
There you go, multiple calendars sync to your device now!
