AMD admitted yesterday that some 780G motherboards are incompatible with its new, high-end Phenom processors. Since then, we've heard from both the CPU maker and Sapphire about which 780G offerings are immune to those problems.
As both companies have pointed out, this compatibility issue is entirely unrelated to the 780G chipset. Rather, since the 780G is a mainstream offering, some (but not all) motherboard manufacturers built their 780G mobos with power circuits that can't handle the 125W envelopes of new Phenom X4 9750 and Phenom X4 9850 Black Edition CPUs. Sapphire tells us its 780G-based PI-AM2RS780G motherboard has no such limitation, although it requires a BIOS update to "recognise the new CPU ID's correctly."
Of course, Sapphire is hardly the only maker of 780G motherboards, and AMD tells us users can check motherboard compatibility info at the System Building and Compatibility Info page on the AMD website. Through that page, we learned that 780G-based MSI K9A2GM and ECS A780GM-A offerings are also compatible with the Phenom X4 9750. AMD's compatibility list for the Phenom X4 9850 Black Edition doesn't include any 780G mobos, however.