Disable the Character Accent Menu and Enable Key Repeat in Mac OS X Lion
If you hold down many keys in Mac OS X Lion, a little popup menu appears showing an accented character selection window. This replaces the long existing default of a repeating key, where if you hold down a key the letter will repeat endlessly until you let goooooooooooo.
If you want to turn off the character accent selector and re-enable key repetition, launch the Terminal and enter the following command:
defaults write -g ApplePressAndHoldEnabled -bool false
You can now repeat keys as usual rather than have the iOS-style accented popup appear. If you want to bring the accented character selector back, use true instead:
defaults write -g ApplePressAndHoldEnabled -bool true
Most apps need to be relaunched for the change to take place.