I've just noticed the Molex's AM3 socket datasheet:
http://www.molex.com/pdm_docs/sd/470998141_sd.pdf
Look the page 2.
It shows that socket AM3 has 941 holes apparently.
extra 1 hole might not be problem, but 2 holes are located differently,
so we will not be able to mount AM2+ CPU on AM3 socket

But of course it doesn't mean that AM3 CPU has 941 pins.
I know Phenom II 945 ES (?) has 938pins:
http://www.xtremesystems.org/forums/...&postcount=651
http://www.hardforum.com/showthread.php?t=1376703
So still it looks "AM3 CPU on AM2+ socket" is OK, but not vice versa