How can I reset the dock?
Using the terminal, you can try deleting your dock preferences, then restarting the dock:

% defaults delete com.apple.dock
% killall Dock


This won't affect the contents of your dock, but it will reset the preferences that you'd normally edit in the Dock panel of the System Preferences.

EDIT: Per comments below, apparently this does reset dock contents for some people, but not for others&mdash;not clear why.