I use the idle count to check if I need to re-assign some dwarfs to a intensive task that is currently on the queue, but that number lately is <10 so I was presuming that my dwarfs are all being productive... nope, they aren't. I counted 24 of my dwarves listening the amazing tale of how a dwarf ceased being the manager of some fort. Apparently it was interesting. Anyhow, are dwarf listening histories and the like supposed to be counted as non-idle?
Yes, the idle counter is meant to show you how many dwarves are sitting around waiting to do something. The new "jobs" like listenting to stories are essentially the new way that dwarves sit around and socialize so the idle counter has become less reliable than it used to be because of how much more common socializing is. My guess is that toady will eventually change it to include socializing dwarves to be a better measure of how many dwarves are working.