it's in a hard spot to find.
go to settings. then calendar/ mail settings
then, in the list of your mail accounts, tap on "add account" and then tap "Other" and then the next screen will show you the option to add a caldav or subscription calendar url.
with copy/paste, adding the url from a note or website is pretty easy.
OR, add the subscribed calendar to your mac and then use itunes to sync it to the iphone.
so, yeah, I installed 3.0 and adding the google holidays calendar subscription via copy/paste was the first thing I tried out. (excitement!)