We recently identified and confirmed what appears to be a bug in the way that .Mac synchronization of subscribed iCalendars transfers the URL of the subscribed calendar to other machines connected to that .Mac account. What we've found is that "simple" URLs transfer from mac to mac with .Mac synchronization just fine, but complex URLs don't make it across intact and appear to be truncated at the first appearance of an "unsupported" character (such as a ?) in the URL.
Most likely, this hint will not apply to the large (vastly large) community of iCal subscribers, but one (ASP-based) site we make heavy use of provides credential authentication within the URL of the calendar, and has a fairly complex and long URL. These calendars make it successfully onto one machine and work just fine locally, but when the .Mac synchronization occurs, the other machines only get a fraction of the URL and the subscription is broken. This starts a vicious circle (because if you fix it on that machine, then it breaks on all the other machines in a subsequent sync attempt).
I've submitted a bug report to Apple for this item, but have also come up with a viable workaround. This hint is intended to help anyone that might be in this same boat at some point and save folks time in troubleshooting (since I wasted enough time trying to figure out the problem for everyone).
I took the long, complex URL and fed it into the TinyURL digester, and out popped a reasonable and very simple URL. Feed that to iCal as the subscription URL and voila! The URL now works across all machines syncing to the .Mac account perfectly. For those who enjoy Dashboard, there's even a Dashboard widget for TinyURL.
Not the most exciting of hints, but hopefully it saves someone else some time, too.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050707165912722