HKEPC.com have a picture and some brief specs of a reference AMD Socket M2 / Socket AM2 motherboard built on the upcoming VIA K8T900 chipset. At first glance it looks like users will have to retire their existing heatsinks for all new ones which are compatible with the new Socket M2 retention frame! The new AMD Socket M2 / Socket AM2 retention mechanism mounts to the motherboard at four screw-points, and has clips which are similar to that of the socket 478 retention frame. The good news is that the frame supports larger heatsinks, so lower noise coolers should be easier to develop.
A CAD drawing of what is allegedly the "reference AMD Athlon64 Socket AM2 heatsink" and "Socket AM2 retention mechanism" surfaced on VR-Zone a while back. Looking at the Pro-E rendering, a couple noticeable changes are visible. First, the reference Socket M2 heatsink is much wider, employs a copper baseplate with four heat pipes, and uses a stacked copper/aluminum fin arrangement. If I had to guess, I'd say the manufacturer was AVC. The official AMD Socket AM2 mechanical design guidelines have yet to arrive at FrostyTech (send the Socket AM2 / Socket M2 specs in if you've got them!), but there appears to be an integrated EMI shield in the Socket AM2 retention frame too. The EMI shield was outlined in AMD's K8 Mechanical Design Guideline, but never implemented as far as we are aware.
The Socket AM2 retention frame mounts to the motherboard with four screws, whereas the K8 version utilizes just two. Noticeably absent is any indication of a PCB stiffener plate on the backside of the motherboard. It also appears as though the Socket AM2 retention frame may be backwards compatible with existing socket 939/940/754 AMD K8 heatsinks (note the center tab on either side).