This bug is caused by the fix to OSDL kernel bug 3022.See description of same symptoms at http://bugme.osdl.org/show_bug.cgi?id=3022#c177.
As explained by comment #178, the boot parameter video=radeonfb:ignore_devlist=1 will disable the fix and thus fix the "hangs on second suspend" bug. However the Thinkpad will then revert to draining the battery quickly in suspend mode.
FWIW my Thinkpad is a 2373-7JU.