Downloaded iPhone 3.0 last night. So far I have like everything. Some bugs but for the most part, everyhing is working. Wanted to post how to setup Google CalDAV.
First go to settings > Mail, Contacts, Calendars > Add Account… > Other > Add CalDAV Account.
Server : www.google.com
User Name : email address
Password : gmail password
Description: Google Calendar
Click save. After it comes back failed, scroll down and click the advance settings.
Use SSL : ON
Port : 443
Account URL : https://www.google.com/calendar/dav/emailaddress/user
Should work after that. Did for me.