The Mac App Store says that 3.1.2 is available.
About Aperture says 3.1.1.
No place to click to install the upgrade through the Mac App Store. Downloading the update from Apple directly results in 'The version of Aperture installed on this Mac must be updated through the Mac App Store. Check the Mac App Store to see if an update is available."
Gotta love mix-ups like this when Apple's left hand doesn't know what the right hand is doing.