2D/3D dock in Lion

To change 3D Dock to 2D dock:

1.Type in terminal as :
defaults write com.apple.dock no-glass -boolean YES

then hit enter key.

2. Then type in terminal: killall Dock
then hit enter key.

To change 2D Dock to 3D dock: 

1.Type in terminal as :
defaults write com.apple.dock no-glass -boolean NO

then hit enter key.

2. Then type in terminal: killall Dock
then hit enter key.