I tested this with SD302 and posted the result on the Audio section.

The camera was 10 dB quieter with line in, even though you have to turn the potentiometers all the way open, which has worried some people. No reason, an amazing dynamic range of 90 dB for in-cam audio!

Link to Petri's audio post:
http://www.dvinfo.net/conf/showthread.php?t=109425

Interesting, and generally consistent with my observations/tests.
In my test of camcorder noise floor, the the camcorder noise floor was about 9 dB better with line input and pots at max, than at MIC ATT setting with pots at mid range, and about 14 dB better than MIC setting with pots about mid range.

Thanks for your post.
Kippis!