use Perl

• You can't double-click URLs
• You cannot drag entries from Address Book; you need to click the "add" icon which opens a new dialog containing the entries from Address Book, and drag from there
• There is no way to select multiple items to delete/recategorize/etc.
• It crashes
• Somtimes when I restart it forgets the names of calendars, or that they were subscribed-to, and I need to re-subscribe
• There's no apparent way to cancel updating a calendar; I had to quit iCal to get it to stop (at least I didn't have to force quit)
• It apparently stores the data on disk in .ics files, which is nice because I can manipulate them by hand, but bad because they are miserable to parse live by computers; I think this is why when I make a change to a large-ish file, it takes so long
• It sucks up a ton of CPU and memory: from 7% to 14% of my 512MB of RAM with about 300 kilobytes of calendar, compared with Palm Desktop, which takes less than half the RAM with twice the amount of calendar data (plus Address Book data), and is about 20 times faster

There's some other things, but the general idea is that it is just way too slow if you have a lot of data. I am considering possibly spending some time taking old appointments out of iCal and moving them to another calendar file to speed it up, but there's no way to do that in iCal itself, even.

By the way, setting up mod_dav to share your calendars is easy. On Mac OS X, I just uncommented the two lines in httpd.conf to enable mod_dav; I made places for the lock file and the dav/ directory (making them writable by Apache); set up the permissions in Apache; and restarted Apache.