AM3 CPUs will run in AM3+ sockets, but AM3+ CPUs will not run in AM3 sockets.
This unfortunately means that you need a mobo upgrade to use Bulldozer, but it also means that the Fusion platform will support mainstream CPUs from the very start.
A bit more on repair/recycling of chips. I don't know a lot about this, a lot of it is hearsay. You're right that repairing a raw die is an astounding technical feat, and it would be impossible to repair a damaged core. However, I do believe that Intel will fix minor or easily fixable problems. Again, bad cache is a good example. If a Gulftown has a bad L3 cache chip, it could easily be worth replacing. Even if it costs the equivalent of $500 to repair, that's still a $200-300 profit off that chip, versus zero if they just trashed it, or less than $50 salvaging and recycling.
EDIT: There's no reason for Fusion not to have PCIe slots/links for discrete GPUs. The onboard GPU of Fusion is supposed to be something like a 5450, or its Radeon 6000 counterpart. Entry level obviously, but far better than anything Intel has shown. The high-end AMD Fusion gaming system of 2011 will be a 4/8 core Bulldozer CPU in an AMD 990FX chipset motherboard with a Radeon 6800 or 6900 series graphics card.