Hi!
After much head-scratching I've discovered that the currently loaded sketch on my new Arduino Duemilanove won't run when these conditions are true:
- the USB cable is connected
- the computer is awake
- the Garmin ANT Agent on Mac OS X is active.
In this situation all that happens is the pre-mounted LED (13) blinking slowly.
This may very well be a bug in Garmin ANT Agent, I don't know. The Garmin ANT Agent for Mac OS X is a piece of software for using an ANT wireless dongle, to communicate with their line of GPS watches.
/Erik