Here is a Blurb from CeBIT. Not sure how accurate this is, as I have not confirmed this against another source...It seems to sum up the compatibility issue.


CeBIT:
The good news is the compatibility of AM2+ quad core processors with current AM2 motherboards. Indeed, according to AMD but also a well known motherboard manufacturer, this compatibility will be effective.

A motherboard with an AM2 socket will be compatible with AM2 and AM2+ CPU and vice versa. Also, according to the same manufacturer, future AM3 processors using 45nm fabrication process and compatible with DDR2 and DDR3 will be compatible with current motherboards. AM2 and AM2+ processors will not, however, be compatible with AM3 motherboards as the latter is restricted to DDR3. Of course, with AM2 sockets, future AM2+ quad core processors will not express their full potential: they will not work with HyperTransport 3.0 but with 1.0, and the distinct voltage between the cores and the memory controller will not be possible.