I tried the steps mentioned but that does not seem to work on Lion. I can still see the dock. Are there hidden defaults that can make the dock invisible or off-screen on OS X Lion?
Yes. You can make it so you don't see the dock by adding a very long delay to the animation so that in practice, you never leave the mouse on the "expose the dock" target long enough to see it.
This is technically a "workaround" since the dock is still there, just slower to appear than we care about on our timescale.
Two steps are needed to set this up.
One, activate auto-hide in System Preferences → Dock → Autohide or type ⌘+⌥+D
Two, open the Terminal an type:
defaults write com.apple.dock autohide-time-modifier -int 100; killall Dock
You're set up now. In this example, it takes 100 seconds for the dock to appear. Make the timer even longer if you like, this long delay eventually helps you to forget that the dock is even there.
Reset to default behavior by typing:
defaults delete com.apple.dock autohide-time-modifier; killall Dock
There's another hidden preference for the delay before the animation starts:
defaults write com.apple.dock autohide-delay -float 9999999 killall Dock
Removing /System/Library/CoreServices/Dock.app/ would also disable Mission Control, Launchpad, Dashboard, full screen windows, the Notification Center sidebar, and the application switcher.