Well, at least Players of D-Day, Gloom and some
other Mods are still very active (when I first
went on the Gloom-Server to Beta-Test the first
working Gloom-exe, there were around 25 people online

). There's now also some Devastation
Q2 Servers again (when I ported it next to nothing happened with Devastation anymore, but this seems to have changed a bit again).
ChaosDM is also still quite active.
But for some other Mods which were well-played
when Q2 was still number 1 in PC-Games not much
is happening anymore.
I think there was some sort of "Q2 Nostalgia" after the Q2 Source-Code was released, though.
It has also to be considered that there are people who think that Q2 Gameplay is better than Q3 Gameplay, so these people never stopped playing
Q2.
Steffen