If you press and hold a letter in Lion, a popup will appear with the various accented versions of that letter. If you don’t use this and want to get rid of the distraction, you can disable it.

1. Open Terminal.

2. Execute the following Terminal command:
defaults write -g ApplePressAndHoldEnabled -bool false

3. Log out of your account for the change to take affect.

If you want this functionality back, simply execute the following Terminal command and log out.
defaults write -g ApplePressAndHoldEnabled -bool true