By default, for some strange unfathomable reason, when you install OS X Lion, the key repeat behaviour is not what we know and love.
From observation and experience, some keys repeat while others don’t, suffice to say that letter keys and number keys don’t repeat.
This is fixable though, and you can restore the usual key repeat behaviour, thanks to this post here.
Open Terminal, and enter the following command;
defaults write -g ApplePressAndHoldEnabled -bool false
Close Terminal and reboot.