<< What does it mean to be "officially supported"? I've heard this response several times. Will they work without issue, or do they have cache coherency problems because they don't "officially" support SMP? >>
They will work and they will run perfectly fine. It merely means that AMD will not provide support for Duron's in SMP, and offer no guarantees of reliability in SMP operation with the Duron... so if you run into problems your screwed.