Comment 11 for bug 39856

I've tried the following workaround, and it works for me across a session logout/login.

Short:
Use gconf-editor to change the value of /apps/panel/toplevels/bottom_panel_screen0/y to the vertical screen resolution.

Notes:
I ran gconf-editor from the terminal. There were other keys for bottom_panel_screen1 and top_panel_screen[0/1] visible, but I tried this one first and it worked for me. When I changed the value to the current vertical resolution it appeared to invoke some magic, because the value automatically adjusted to put the panel at the bottom of the screen: I typed "1024", hit return, and a split second later it said "975" where it used to say "1024". The calculation appears to be ((Y resolution - Panel size) - 1). Panel size is visible in the panel properties dialog. As soon as the new value was entered, the panel moved to the new position, and I quit gconf-editor.

Thanks:
Originally found in dbloom's post at http://ubuntuforums.org/showthread.php?t=117997