I'm looking for a site where you can look up a sentence you're having trouble with and discuss it, read old discussions about it. Maybe link to relevant grammar points, read about weird usages of words, how context affects things in non-obvious ways?

E.g. say there's a sentence in KO2000 that I don't understand. Presumably this is often not because I'm a retard, so maybe other people have asked about it too? Especially earlier in my studies I often had a bunch of sentences that I wanted to ask someone about, most of them from some popular text book, online dictionary etc.

I mean I realize I could just ask about a sentence by posting on this forum, but is there anything better?

JGram is a Japanese grammar wiki. It has lists of grammar patterns with example sentences and discussions.

http://forum.wordreference.com

Go to the Japanese section.

@Sebastian
But that's only for the sentences in that guide.

@ahibba
Well that's better than nothing. However, I was rather thinking of something akin to a wiki, or a database. Something more organized, like with the stories on the RevTK site.

I was thinking like, if I start reading some popular book (like Ranma, Death Note, Harry Potter or Haruhi), I could just look up any sentence from it that I'm having problems with, and it'd hopefully already have been discussed before.

Then again, in the end I guess just googling might be an acceptable strategy.