iPod songs all show as -0.00 seconds long
I've had issues with an iPod nano showing most songs with incorrect durations, though in my case they were shown as much longer than the song actually was.

My guess is it was caused by encoding the MP3s in a program not called "iTunes".  They played great everywhere, but the song length never looked right in iTunes on my Mac, either.  I guess Apple's MP3/ID3 decoder is stricter than my encoder was.

If you were using some other program to encode them, you could try re-encoding them in iTunes.