Pixologic announced the release of ZBrush4 R2b in in the second half of December 2011 as an free update for all registered users. According to Pixologix the release of ZBrush4 R2 was tested by their users on many different system configurations and workflow, by this they found 'rough corners' which we would like to polish. Even that the patch should fix issues with the new features found in ZBrush4 an official announcement of fixes is not available yet.
Pixologic included into the new version a lot of new features from which the most interesting is DynaMesh, the new base mesh generator, will allow you to realize your concepts via a workflow that ignores the traditional geometry barrier.
Source and full article: Pixologic