Xbox Product Managment Director Aaron Greenberg says: "they've put the worst behind them, and performance of the current systems are strong."
Looks like Microsoft have upgraded the specs inside the box. Apparently Greenberg can't talk about the exact specs of the fixed 360s because Microsoft's attorneys would not allow him to, but we do know that there was a new "jasper" motherboard released at the end of 2008. Attached to the motherboard is a new 65-nanometer graphic chip. The new chip consumes less power and runs cooler, also looks like it is preventing the RROD in the newer consoles!