I haven't upgraded to Leopard yet, but it seems a full reboot wouldn't be necessary. There's a way to restart the dock. Just type killall Dock in the terminal.
Note: I don't remember exactly what the command is. Capitalization might be different. Could be "Killall Dock" or "killall dock", but I think it's like I said in my original post, with Dock capitalized.
EDIT: Also, if you use MainMenu, a maintenance app, you can use that to restart the dock.