I run Poser 11 Pro on a mid-2010 iMac. When I installed the update, my library palette disappeared as well, and when I relaunched again, it finally came back after about 10 minutes...

On a related note: One thing I continue to hate about all Poser updates is that they don't remind you that it is going to wipe out your libraryprefs file. Luckily, I save them periodically, but there are always some recent things that I have to re-add. A simple message - back up liraryprefs before installing - would save a lot of people grief.

And I also find that when I add a new library folder from an external runtime, I have to relaunch to add a second one (and so on and so on).