I had a strange problem with my Mac (OSX 10.4.4) this morning–the Dock wouldn’t “unhide”. Normally I keep the Dock hidden to save screen real estate, and when I need to fire up one of my usual applications I just drag the mouse down to the bottom edge of the screen and voilà, the Dock pops up with all of my favorite apps. But this morning the Dock was being shy and wouldn’t reveal itself. I tried toggling all the preferences, but nothing helped. I finally found this suggestion on Apple’s Finder, Dock & Dashboard discussion site (registration required, or read my version of it here):
Delete (or move/rename) the com.apple.dock.plist in your ~Library/Preferences Folder, then log out and log back in. This worked for me, but I lost my Dock settings, in particular the applications that were in my dock! It seems obvious in hindsight, but I suggest that you make a list of your docked applications before you whack the preferences file, so you won’t have to repopulate your Dock from memory.