teckel:
Interesting... Find the attached TestB - TestE libraries and test with the same sketch. Each of these make slight changes and all work with the Uno. Let me know if you start getting correct results (objects several inches from the sensor should give results in the hundreds). It's still possible that none of these work for you, and if so that REALLY limits what the issue is, and I have a TestF library already ready to go.
A rebuild with each version (exit Arduino IDE; unzip a test version of NewPing inside ~/sketchbook/libraries/NewPing/; run IDE; load test sketch; upload to Duemilanove; open serial monitor) still outputs 0 uS, regardless of whether or not something is close to the sensor. I can run each version for more time to see if I get any nonzero times, but I thought I'd report these results sooner rather than later.
I'm pretty sure my steps will explicitly re-build the NewPing library each time, but maybe I need to touch the sources, too.