There is also www.jazzguitar.be/forum/
Like all groups of humans it has its strengths and weaknesses. The
biggest strengths are general civility and a very diverse participant
base, as well as active moderation to manage incivility. The biggest
weakness is scarce participation by practical masters such as Jimmy
Bruno and Tony DiCaprio, who do post here from time to time- although
ISTR both of them posting there once or twice as well as a few others
such as Frank Vignola, but they are not regulars by any means. Tim Lerch
is also a contributor.
Jimmy B also has an online school, Frank has an excellent series of
instructional videos online and Tony does highly informative (and
entertaining) Skype lessons. There are other online options for
learning from great musicians- master classes with Peter Bernstein, for
example. Jimmy posts near-daily entertaining/curmudgeonly and sometimes
politically incorrect rants daily on YouTube, which are often
interspersed with solid musical information. (I don't know if it was
intentional on his part, but the videos have also documented his amazing
recovery from severe health issues that threatened his life and ability
to play, back to being an on-fire musician. That has been heartening
and inspirational, even when I find myself disagreeing with his
outbursts of curmudgeonness. Is that a word?).
And, heck, even this newsgroup is still helpful sometimes!