If anyone has an elegant solution to extending gnome panels over multiple monitors, please let me know!
I other news, if you have two monitors and stack them with the panel on the top of the bottommost monitor, you'll discover how gnome handles hiding panels. Set the panel to auto-hide and it'll just slide up to the bottom of the top monitor! That's not hiding my panel anymore, that's just making it really hard to control the screen layout.
More and more I find myself just using a whole pile of screen sessions and putting jobs in the background...this makes for quite a mess when I need to reboot.
Also, if you have one of those convenient USB hubs on your monitor, make sure that you know which one your keyboard and mouse are plugged into before you go shutting off monitors!