Usenet is still around but mostly for binaries. The market's of pretty stable size, dominated by a few large wholesale players.
My take on what happened with text groups is that the S/N ratio just went to hell. In the 90s the problem was spam, but in the 2000s the problem was too many loudmouths who wanted to hear themselves talk drowning out the useful experts.
Like some of the other folks commenting, I've been pissed as hell at the PHPBB/vbulleting monstrosities. My original plan with readnews was to try to build a great web UI for discussion, but we got distracted by wholesale customers wanting service - and front-end is not my area of expertise.
For folks looking for something modern with promise, the news is good with discourse and a few others coming up. Would love to see something distributed, but if really distributed I suspect we'd see binaries and/or commercial spam and/or people with nothing interesting to say dominate - just like Usenet...