Parallels 2.5 was updated to build 3212. The previous production build was 3188. The update is available through the Parallels automatic update feature and is not related to to Parallels Version 3 which is new.
The upgrade is via a downloaded disk image file (.dmg) which you then need to open and run the installer. The download seems to be a full install. I couldn’t find any trace of a change log or mention of what’s included in the upgrade. So your guess is as good as mine. The build number increment is small so it’s probably just bug fixes or performance improvements. I had to work around the Ubuntu install so maybe this version fixes that problem. I’m not curious enough to spend the time trying to see if it was.
The update contains the following changes:
1. USB compatibility patch for upcoming Mac OS X 10.4.x/10.5.x USB update.
2. Improved autoupdate module which separate future updates of 2.x and new paid upgrades of 3.x.
I upgraded all my VMs (Windows XP SP2, Vista Ultimate and Ubuntu) started without complaining but I haven’t used them for any length of time.