Default calendar app does not show all my online Google calendars
Not all calendars are allowed to sync with the google calendar app - examples of this are NFL schedule calendars. Any calendar that are not in the XML format will not sync. I remember seeing a warning about some of the interesting calendars not being able to be synced with my phone when I first set some of them up.

Here is post with a work around on how to get them on your phone - if this is your issue:
http://www.google.com/support/forum/p/Google+Mobile/thread?tid=70374da8b32c29e4&amp;hl=en