Hi Rick,
Interesting thread. I thought neta just meant joke (funny story). But now I think about it I have heard it in the sushi context to mean the fishy bit. I've never seen it used to mean "(mailing list) troll" - I'll keep my eyes open for that in future.
I'm still struggling to see how the meaning of neta relates to the meaning of "tane". Well, a troll seeds a conversation (though I believe troll always has a negative meaning - does neta?)
The only JMDict entry seems to be:
ネタバレ: something that spoils the ending of a story or movie
(from ばれる)
Darren: I see "neta" all the time these days, and it's funny because I've been here for a while but only started to notice. I don't think it has anything literally to do with a 'seed', per se, but more the gist of something, perhaps (the seed of an idea, say). As for mailing list troll, I don't know what to say. Maybe a kind of Katakana of some kind of internet person known as a "netter", though then it would be 「ネター」you would think.