AMD managed to pull one small miracle. The first 45nm native quad-core from AMD labs, codenamed Deneb and Deneb FX, will be native socket AM3.

However, AM3 will have an identical pin out as socket AM2+ (Socket 940) and if you plug Deneb in Socket AM2 it will work as a DDR2 chip, and if you plug it in socket AM3 it will work as DDR3.

This will be very convenient, as it will make transition easier. This will be the first time after many years that AMD has decided to make an easily upgradeable CPU environment. In the past when AMD changed the memory support that would mean a new motherboard and a new CPU but this time moving to DDR3 will require a new motherboard, but the same CPU will work in your old DDR2 socket AM2+ board and the new DDR3. 

The timing makes sense, as AMD needs to make Deneb (and later Propus) as sexy as it possibly can, as this much delayed chip will have some nasty competition in the guise of Yorkfield and Nehalem to fight. Sometimes working under pressure of fearsome competition results in a pleasant surprise such as this one.