Lost Circuits :

All Bobcat and Bulldozer enabled motherboards based on the AM3+ socket will be backwards compatible with earlier AMD AM3 CPUs but AM3 CPUs will not be a drop-in replacement for existing processors in existing motherboards.
ExtremeTech :

AMD also told us that it will introduce a new AM3+ socket for consumer versions of Bulldozer CPUs. AM2 and AM3 processors will work in the AM3+ socket, but Bulldozer chips will not work in non-AM3+ motherboards.
I don't understand what Lost Circuits's words means