defaults write NSGlobalDomain ApplePressAndHoldEnabled -bool false
and while you're here, check out these other fixes:expand the save dialog by default:
defaults write NSGlobalDomain NSNavPanelExpandedStateForSaveMode -bool true
defaults write NSGlobalDomain NSNavPanelExpandedStateForSaveMode2 -bool true
don't save .DS_Store to network locations defaults write com.apple.desktopservices DSDontWriteNetworkStores true
bring up the hidden dock faster defaults write com.apple.dock autohide-time-modifier -float 0.15;
Shut up gatekeeper spctl --master-disable
I had almost forgotten how much annoying manual fixes you need to make this system usable, until I went through my notes...