Installing from a .pkg or .mpkg file on Mac OS X Lion
The update did not work for me, as I had already run it. It broke after the update. I still had the problem. In Finder, I could see that the file extension icon was not the gold/tan box icon that goes with Installer. There are two ways to do this. 1) In Finder, right-click, or get to the property window, and "Open With" and navigate to /System/Library/CoreServices/Installer.app. There is a checkbox to always open with this app. -or- 2) Open Installer itself and drag the mpkg file into it. Run the installer.

Both of these should run, and also change the mpkg icon in your Finder.