Yeah, b117 has a number of problems, XAA crashes Xorg (which is exactly what you are observing) and with EXA all X events are very very slow which makes X unusable. So I'm just like you, using the VESA driver. See http://defect.opensolaris.org/bz/show_bug.cgi?id=9750
(Lenovo T61 here as well) -- This message posted from opensolaris.org
