westfw:
The bootloader does flash the LED upon power up, though
This is odd too. Assuming that you're using Optiboot, the bootloader should not run, and it should NOT flash the LED, on powerup. This is the "Adaboot fast start mod" that starts the sketch immediately on powerup, and only attempts uploading based on an "external reset."
Any chance that this somehow contains the wrong bootloader?
There is always a chance I have the wrong bootloader. I am using unadulterated IDE 1.0, choosing Uno as board and Arduino as ISP as programmer, then Tools/Burn Bootloader. Have followed same procedure with dozens of chips/boards, so I hope there isn't a problem 
Here's the behavior I am seeing with multiple "good" chips:
- 3 LED flashes on connection of USB cable
- 3 LED flashes on DTR during IDE sketch upload via USB
- 3 LED flashes on pressing reset button
- 3 LED flashes on connection of 9VDC to power jack (no USB connection)
With the one "bad" chip, I am seeing this:
- 3 LED flashes on connection of USB cable
- no LED flashes on DTR during IDE sketch upload via USB, followed by upload failure message
- no LED flashes on pressing reset button
- 3 LED flashes on connection of 9VDC to power jack (no USB connection)
Jim