I have FC1 on a Dell i8100 and i8200, both with nvidia video using the
'nv' driver only. When Gnome starts up and the icons on the Fedora
splash screen finish drawing a black bar appears over a large part of the
gnome-panel (bottom-edge). It disappears after about 1-2 seconds and
everything works normally afterwards.
I believe this is one of the panel applets (probably the window list) starting up. No idea why it colors itself black momentarily. Could the panel allocating space for it.