In case you were considering to update to either Joomla 2.5.12 or Joomla 3.1.2 – Wait!
Both releases are having some problems, which will be resolved with the next release. The next versions will be tagged as 2.5.13 / 3.1.3. These releases will be made available in the near future.
So, for once, ignore the lure to update immediately, and skip this version. In case you already upgraded, and your site might work less than stellar – did you remember to create a back-up?