I've got 94 listed, in 8 different groups. Of those groups, one containing 23 hasn't been updated in 127 days, so I guess I really only use 71. I suspect a lot of those are probably not that active anyway; I should probably do a pruning at some point.
Unlike a lot of people here, I do download the headers, rather than use indexing sites, because a lot of what I use newsbin for is downloading foreign language stuff (jdrama, that sort of thing). Most of the stuff I learn about either from my friends overseas or from perusing the group listings themselves. I can't really use a search, since I don't know what I'm looking for ahead of time. It's more of a "hmm, that sounds interesting, what is it" sort of thing.
Because of the translation issues, I never know what a series will be called. For example, one series was called "Investigator Mariko", but was also posted as "Kasouken no Onna", "Shin Kasouken", or "Woman of the Crime Lab", depending on the translator (it differed season to season).
What I do is download the headers for, say, a.b.m.japanese, see what's available, and then Google or check a specialty site like
http://wiki.d-addicts.com or
http://www.jdorama.com for a writeup to determine if it's worthwhile.
One feature I would like to see in v6 is a multi level sort or filter mechanism. For example, sort by poster, and then within that poster, sort by date, or by file name or title. Unfortunately, a lot of posters use the default post engines, so they have the same poster name. So it's common to have poster Yenc-Powerpost post something I'm interested in (like Shin Kasouken or Bloody Monday), and then a few days later another poster, also using the same default name of Yenc-Powerpost, posts a bunch of unrelated and/or spam messages. They are clearly identifiable if sorting by date, but sorting by date shows everything by all posters interleaved. If I could filter all posters by name, and then sort within that sublisting, it would make things a lot easier.
Btw, I've been using newsbin for at least six years or so, and I've been very happy with it.