Optura Specs
 

I just visited the canon dv site. I did a spec comparison between the optura 3, 4, and 500.

There doesn't seem to be any. Except 4 and 500 shoot with less light in nite mode.

What gives?

You can also make a comparison on my page at http://www.dvinfo.net/canonoptura/articles/compare.php.

You're right, there is not much internal difference. The biggest change from the 300 to the 400/500 is one of form factor and ergonomics, and battery type. And the on-board light on the 500 is much brighter.

The 300, for the price seems like a great travel camcorder. Manual audio control and uncompressed 16:9. I'm impressed. Can anyone comment on the sound quality of the camera?

Jeff Keller of DV Spot reports that the 300 does not suffer from camera motor noise. See his review here. Otherwise the audio quality is 16-bit as most other DV camcorders are; you'll probably want to use an external mic though.