I doubt that sleep/hibernation works in FreeBSD/PC-BSD!
In the german www.bsdforen.de
it's known that it don't work. And yes, on my Athlon64 X2 Tower with Radion X1550 video card it don't work too. So its not a special problem of your Thinkpad!
You should try Stand-by, that consumes some energy but it works most time.
On my Athlon64 X2 the wake up from stand-by makes my USB-mouse not work. I must plug-out my mouse an plug-in again to work. But my USB-keyboard (in USB-keyboard) works always after wake-up.
But better than full reboot.