Mac OS X (10.5.6) only: Instead of launching iCal and clicking on a date to add something to your calendar, Macworld details how to put together a one-click Automator action. With a simple New Event Automator app on your Dock (or accessible to your favourite keyboard launcher), you can add an iCal event or a new to-do in one shot, with the ability to add event details on the spot. If you've never used Automator before, don't worry, because putting together this one is a cinch. Apparently this tip didn't work in OS X 10.5.3 through 10.5.5, but yesterday's 10.5.6 Software Update fixed the bug and it works again. Here's what the new event dialog looks like when you launch the Automator applet:
When you hit Continue, iCal launches (if it's not running already) but doesn't steal focus, so you can keep doing what you're doing.