Here is how I made it work yesterday:
- Visit (in a desktop browser) the URL http://m.google.com/sync
- Under "Google Sync Setup Instructions," find iPhone, then click "Read Setup Instructions"
- It should take you to the page: http://www.google.com/support/mobile/bin/answer.py?answer=138740&topic=14252
- Follow the instructions until you reach the bottom of the page, then click on "choose which calendars to sync." (On that page, if you have a Gmail account, follow the instructions in the top section; if you use Google Apps, follow the instructions in the bottom section.)
- When instructed, visit (in the iPhone or iPod Touch Safari browser) either http://m.google.com/sync (for Gmail users) or http://m.google.com (for Google Apps users).