Really, to be honest, C & C seems to be a fairly lost art. Most people on a ML
tend to remain silent because they want something to read, but don't want to
share their writings. :)

Taking the DnR mailing list as an example,

Most posts there are usually either 
A) drafts of episodes
B) people asking for MORE episodes
C) debating on certain plot elements of an episode.

C is a lot rarer. I've noticed most people who comment are themselves also
writing fanfics (or started.)

I'm going to presume something: People who tend to comment are themselves
writing fanfics, and as such, have less time to devote to C & C'ing others'
fanfics because they're too busy driving themselves nuts nit-picking their own
fanfics.

Heck, I don't think we really got a FLOW of C & C on the DnR mailing list very
often, and those who took the time to comment were very appreciated. (Even the
guy who gave me an headache trying to figure out the sun/moon/stars' positions
in one fanfic. :) ) But it took a long while to get people to be WILLING to
tear apart the fanfics, probably because they need to judge how the authors
will response to criticism. 

Oh yes, one other thing: Keep writing. It's the only way you're going to FIND
somebody sooner or later who WILL C&C. My first fanfic (Monkey Business) was
met with a resounding silence. :) Unfortunately, I was stupid enough to decide
to keep trying, and my next fanfic was DnR #1. (Okay, so the only comment I got
about it was from John Biles, who called it an abomination or some such thing.
:) ) I worked on #4... and then I think I hit my stride with #6. Somewhere
about then, C & C started rolling in.

-D.

P.S. BTW, Zen, I've been meaning to ask you, but never did get a chance to: Did
the big discussion over Ukyou's portrayal in DnR as opposed to Takahashiverse
lead to that very good Ukyou portrayal in your fanfic? Certain elements in that
discussion appears to have carried over into the fanfic you wrote.