Looks like several people are having this problem.
When I go to edit (or create) a new page, I cannot use the visual editor - I have to use the text version. Visual editor does not produce a window that you can type into - just a blank area where the box should be.
I have reuploaded the WP Includes folder, and also tried reinstalling the update via the Updates tab in the admin window. Saw some suggestions about disabling plugins - going to try that next, but just checking to see if anyone has actually found what is broken in the update to cause this problem on some sites.
My question is, is it possible to downgrade back to a version of wordpress that works, without destroying the site?