In Mac OS X 10.8.2, I have this curious problem. Every time I install a new updated version of one of several applications that I use, my system adds a new duplicate entry in the "Open With" contextual menu:
I have tried clearing caches and rebuilding disk permissions and rebooting, but the problem persists.
I have completely rebuilt the Launch Services database and completely rebuilt Pre-Binding, more than once, by using the standard command line tools and using two different commercial cleaning utilities to do the same thing.
I have also deleted and rebuilt Spotlight and then rebuilt Launch Services and cleared caches again.
Nothing has any effect.
It seems there have been similar questions posted here before, and all of them are incorrectly answered by "Rebuild the Launch Services database" but that does not help the problem.
Update 18 January 2013
After filing a bug report with Apple, I have received a notification that this is a known bug that they are already tracking and working on. It is Bug ID# 11582257, for anybody who follows these things.
Update April 2013
This bug has not been fixed in Mac OS X 10.8.3.