Data Detectors allow you to turn addresses, phone numbers and dates in mail messages into Address Book contacts and iCal events. You can also turn selected text into to-do items or stickies.
iCloud makes it easy to share calendars with others. You can create a public calendar that is read-only to others and anyone can subscribe to it. You can also create shared calendars that can be viewed and/or updated by a list of others you invite.
In addition to being able to create events in iCal, you can also create items that are not attached to a specific date and time. These to do items, or reminders as they will be called in Lion, can be simple items that you can check off, or they can have priorities and alarms attached to them to help you organize.
If you add birthdays to your contacts in Address Book, it will create a special Birthdays calendar in iCal. You can use this to keep track of your friends' birthdays, although functionality is very limited.
Instead of letting iTunes update podcasts every hour or in the middle of the day, you can schedule iTunes to check at night. Using a simple AppleScript and scheduling it to run with iCal you can have new podcast episodes waiting for you when you get to your Mac in the morning.
You can create tasks in Automator and then have iCal run them at a specific time in the future, or even as a recurring event. This example shows you how to have thumbnails of new photos automatically sent to an email address every week.
Snow Leopard includes a new version of iCal that lets you edit events in two new ways that make it much easier to use iCal as your calendar program. You can also easily import and sync Google and Yahoo calendars.
You can publish your own iCal calendar to MobileMe or to your own hosted server. Others can then subscribe to your calendar. It is a great way to make a list of events available to others.
Learn how to connect iCal to your Google Calendar. You can add events and update either one and they will synchronize within minutes.
Gary Rosenzweig shows you how you can subscribe to free and interesting calendars using iCal.