Both Joomla 2.5.13 and 3.1.4 were released this week.
Remember that updating Joomla is now as simple as logging in to your Joomla site and clicking on the flashing icon that notifies you of an update.
Both of these releases are regularly scheduled maintenance releases and only provide bug-fixes. There were no security patches.
Updating immediately is recommended but not absolutely essential.
Joomla 2.5.13 Details
Joomla 3.1.4 Details
Problems with these releases
These releases were due to be 2.5.12 and 3.1.2. However, the release packages were accidentally made public before the launch and people started updating with Admin Tools. The developer of Admin Tools had an explanation of what happened, as did the Joomla team.
These accidental updates left a good number of sites on Joomla 2.5.12 and Joomla 3.1.2, even though those versions didn't officially exist! So, those versions were skipped. There was then a problem with Joomla 3.1.3 which lead to the release of 3.1.4.
Got all that? Good!
Confused? Don't worry. If you're on 2.5.13 or 3.1.4, that's really all you need.