There’s more information about Denebs and what it will/won’t run.
Deneb has a combo memory controller so every chip should support DDR2 and DDR3 but at this early stage, we understand that we will see different versions of the chip – one supporting AM2 and another AM3. Its a bit fuzzy how AMD plans to do that but we know you will need the latest 790GX and 790FX+SB750 boards to make them [work].
In other words, they do and it won’t. The chips series will support DDR2/3, but any individual CPU will support one or the other, not both.
For those of you who like to incrementally upgrade your system and thought these chips would give you a lot of flexibility (like buying an AM3 chip to run in an AM2+ mobo, then buying an AM3 mobo later), it doesn’t look like you’re going to be able to do that. I hope not too many people got burned buying products assuming they could do that, and there’s no reason at this point to buy under the same assumption.
Perhaps a bit worse, this talk about needing very recent AMD mobos to get them to work isn’t good news for those with slightly older boards (though this might be a reference to getting them to work fully per AMD Overdrive/Fusion).
Again, when in doubt, don’t until there is no doubt.