Since the introduction of Lion the system’s Software Opdate mechanism has been integrated into App Store.app and the Software Update Preference Pane has been removed and substituted with “App Store”.

If you constantly are being reminded to install software updates you don’t really want to install, you can right-click (Control+click) the name of the update and hide it, eliminating the reminder.

[crarko adds: I think this is probably known already to many of you, but if it’s not it can be a handy trick. I find the whole App Store method for Software Update a lot less pleasant than the old Snow Leopard mechanism where it was separate, but maybe I’m just old fashioned.]

Source: Mac OSX Hints