From the Apple support site:
Syncing calendar subscriptions
Symptoms
iCal can subscribe to various calendars, including some calendars provided by Apple or published by other MobileMe members. When syncing iCal data with MobileMe, you may see some unexpected results:
When syncing subscription calendars between a Mac and an iPhone/iPod touch wirelessly via MobileMe Sync: Subscription calendars do not appear in your iPhone/iPod touch.
When syncing subscription calendars between a Mac and a Microsoft Windows-based PC: Subscription calendars do not appear in Microsoft Outlook 2003 or 2007.
When syncing subscription calendars between a Mac and MobileMe Calendar: Subscription calendars do not appear on MobileMe Calendar.
When syncing subscription calendars between two Mac OS X 10.5-based Macs: After adding a calendar subscription on one Mac and syncing to MobileMe, events for that calendar may not download on the second Mac until you open iCal. As a result, if you are syncing a device (iPhone, iPod touch, and so forth) via iTunes with the second computer, the calendar subscription events may not sync with that device until after you open iCal at least once to download the events.
When syncing subscription calendars from a Mac OS X 10.5-based Mac to a Mac OS X 10.4-based Mac: If the calendar is not set to automatically refresh, the subscribed calendar may not automatically download the calendar events when first opening iCal in Mac OS X 10.4.
Resolution
Syncing from one Mac to another
If you have just subscribed to a calendar on one computer, and you are syncing calendar data with another Mac, open iCal on all other computers that you are syncing calendars with and allow the events to be downloaded. If the calendar data does not download automatically, you may need to refresh the calendar.
Syncing to an iPhone/iPod touch, or with a Windows-based PC
This article will be updated as more information becomes available.
Additional Information
Mac OS X 10.4 and Mac OS X 10.5 handle calendar subscriptions differently, both in iCal and in syncing with MobileMe.
Mac OS X 10.4: Subscribed calendars are listed along other calendars, and are denoted by an arrow icon in iCal. When syncing subscribed calendars, the calendar information and settings, and all of the events, are synced to MobileMe.
Mac OS X 10.5: Subscribed calendars are listed in their own section of the iCal calendar list. When syncing subscribed calendars to MobileMe, the calendar information and settings for the calendar is synced, but all of the downloaded events are not. This is done to help streamline the syncing process with MobileMe, as it prevents syncing redundant information to other computers with an Internet connection.
Disclaimers
This document will be updated as more information becomes available.
Third Party Affected Products
Mac OS X 10.4, Mac OS X 10.5, iCal, iPhone, iPod touch