If the 3D Dock isn’t your taste, you can use Terminal to switch to the 2D visual implementation.
defaults write com.apple.dock no-glass -boolean YES
Restart Dock with the following command:
killall Dock
Revert to the default setting:
defaults write com.apple.dock no-glass -boolean NO
Restart Dock
3D
2D
Screencast:
sadly, no longer works in Mavericks