Joomla 2.5.5 has just been released.
However there appear to be issues and bugs that have already been reported and Joomla 2.5.5 has broken CB 1.8 user saving process.
At this point we must recommend that existing Joomla installation should not upgrade to Joomla 2.5.5 and wait for next (hopefully soon) Joomla 2.5.6 release.
The CB Team is temporarily dropping all current in progress activities to work-around these Joomla 2.5.5 issues and to release a Community Builder 1.8.1 package as soon as possible.
[UPDATE 1] A quick fix for Joomla 2.5.5 breaking the CB 1.8 user save is now provided here.