Dean Takahashi, who has previously written two books on Microsoft's consoles, the 65nm processors will probably start finding its way into new Xbox 360s by the end of the year. However, there are a few caveats.
The chips, which are a sizable difference than the current 90nm chips, are being planned for a new motherboard codenamed Falcon (if you recall, Microsoft's previous motherboard upgrade that included an HDMI port was called Zephyr). The upgrade will still have 90nm graphics chips from ATI -- that upgrade is for later. And there is no guarantee that the smaller chips, though theoretically will require less energy, will alleviate the Xbox 360's Red Ring of Death.
And so how will you tell if the console has the Falcon? You can't -- not at first, anyways. "Microsoft has no intention of telling you which box has 65-nanometer chips on the inside," he said. All Falcon-equipped Xbox 360s have HDMI ports, but not all HDMI-enabled 360s have Falcons. "I really don't know how you're going to be able to tell the difference. If you're buying an Xbox 360 without HDMI, then for sure you aren't getting Falcon," he said.
This Christmas, if you're hoping for a more reliable Xbox 360, there is a chance you could nab one. From what Takahashi has said, however, you might have to increase your Luck stat before you try to pick up one. Check out Takahashi's article for more details.