Google added a new ‘snooze’ feature for pop-up notifications in Calendar. You can click on "remind me again in 5 minutes" in Google Calendar's web interface. "When alerted to an event via a pop-up notification and dismissing it, the calendar interface will show you an option to remind you again shortly. Click on that link if you want to be reminded of the event again," explains Google. Also available in Windows-based Google Talk Labs Edition for Google Talk that shows Google Calendar notifications.