OS X

Locations of startup items

/System/Library/LaunchAgents/
/System/Library/LaunchDaemons/
/Library/LaunchAgents/
/Library/LaunchDaemons/

Hide desktop icons

defaults write com.apple.finder CreateDesktop -bool false
killall Finder

Auto-hide other windows on dock switch

defaults write com.apple.dock single-app -bool TRUE
killall Dock

defaults delete com.apple.dock single-app
killall Dock

Flush DNS

killall -HUP mDNSResponder   # 10.8+
dscacheutil -flushcache      # 10.7 below

Turn off spotlight

sudo vim /etc/hostconfig  # change SPOTLIGHT=-YES- to SPOTLIGHT=-NO-
mdutil -i off /