Leopard is smart—smart enough to recognize dates within the text of an email in Apple Mail.
When your cursor hovers over a date in the body of an email, a dotted rectangle surrounds the date, and a small arrow appears. Hold on the arrow, and up pop two iCal options: Create New iCal Event and Show This Date in iCal.
Choosing Create New iCal Event generates a dialog box. Its default name is the subject line of the original email, though you can change it here. You can also specify the location and duration of the event and add additional notes. When you’re finished, choose Add to iCal. Leopard adds the date to your calendar—without even opening iCal.
Not sure if you’re available? Choose Show This Date in iCal. This opens iCal at the date in question, but doesn’t add the event to your schedule.