As of late I can't uninstall any Mac App Store apps once they've been installed.
I follow the standard procedure of opening Launchpad, pressing Option ⌥, and clicking on the little x on the top left corner of the app's icon.
What happens is that the icon vanishes for a second, and then reappears in Launchpad.
This is a typical error I get in the Console right after trying to uninstall an app:
LaunchPad: Uninstall failed Error Domain=com.apple.uninstalld.request Code=2 "ErrorMissingBundle" UserInfo=0x7fa12509b4f0 {Missing bundle string=/Applications/OmniFocus.app} file://localhost/Applications/OmniFocus.app/
I am running Lion (10.7.4).