It seems to behaving fairly well in Mozilla 2.0, but it doesn't work at all in Safari (popup never even appears).
I just tried the newest snapshot (richfaces-3.0.1-20070322.000322-9.jar) and it seems that the rendering and modal problems on IE are gone now (the panel is modal if displayed and always stays on top of other components).
But now, as for my example code, the value in the backend bean that i whish to set is not updated anymore... (both in IE and FF)
btw... amazing components are available in the richFaces lib...
In order to avoid a bug in IE, we move the root node of the dialog on the top of DOM tree. However, you have to have a separate form inside the modal panel because, it is not inside the h:form you declare it on the page.