Comment 7 for bug 681101

Fixes for panel and launcher placement are going to land soon in trunk. Mostly it's about having the same code path used in both cases and cleaning it up a little bit. It does not take into account the multi monitor case mostly because the struts are badly set.

"Struts MUST be specified in root window coordinates, that is, they are not relative to the edges of any view port or Xinerama monitor.
[...]
 Another example is a panel on a screen using the Xinerama extension. Assume that the set up uses two monitors, one running at 1280x1024 and the other to the right running at 1024x768, with the top edge of the two physical displays aligned. If the panel wants to fill the entire bottom edge of the smaller display with a panel 50 pixels tall, it should set a bottom strut of 306, with bottom_start_x of 1280, and bottom_end_x of 2303. Note that the strut is relative to the screen edge, and not the edge of the xinerama monitor.
"
from http://standards.freedesktop.org/wm-spec/1.3/ar01s05.html paragraph _NET_WM_STRUT_PARTIAL