Apple - Trackpad gestures stop working

In 10.8, running killall Dock seems to bring back trackpad gestures.

When a reboot didn't fix this, I went to System Preferences → Trackpad → More Gestures and changed

• Mission Control to ‘Swipe up with three fingers’, and
• App Exposé to ‘Swipe down with three fingers’.

Those gestures now worked with 3 fingers. Then I changed it back to ‘Swipe up/down with four fingers’ on both and they started working again using the four-finger gestures.

If resetting the necessary prefs does not help but the Magic Trackpad is still connected, this is a beautiful alternative: BetterTouchTool

In fact, this is much more fun since it makes the Magic Trackpad so powerful.

http://www.boastr.de/

This started happening to me on my early-2013 MacBook Pro since I upgraded to Mavericks. It happens both and with and without the Magic Trackpad.

Based on the note at the end of Andrew's answer, I ran killall Dock from a Terminal window and the gestures started working again.

This blog post has more information about the issue and there is an Alfred extension to fix it too.