Hi to all on this thread,
same problem here - MAC Pro updated to 10.7.5 - no right mouse button with mighty mouse any more. I installed the supplemental update some days ago, this didn't change the misbehaviour.
I own three mighty mice - with none of them the right mouse button works. When I use the CONTROL-Key - as if I had no secondary mouse button - then the secondary mouse button menu shows up.
Yes, I checked all the features in the mouse-pane.
Very strange is the fact, that with a very cheap mouse by "Trust" the right button works fine! The mouse pane does not show a feature to change the behaviour of the secondary button for this mouse. Maybe this makes a difference?
APPLE please there is to come another supplemental update :-) Go to work! It is your own hardware, that doesn't work!