Application Switcher is minimizing apps At some point when I reinstalled Mac OS X Lion, the application switcher started minimizing apps so that when I switch to one all others minimize.  

This causes problems when working with my developer IDE and a browser. Many times throughout my day I want to look at two or more applications at once.

How can I fix this?
You probably enabled a hidden preference for the experimental single app mode. It can be undone with:

defaults delete com.apple.dock single-app
killall Dock