i've seen this topic several times so i guess i'll post here finally
back when i was a newb i showed the game to a few of my friends, everyone liked it or thought it was cool, but none of them really kept playing after the first time i got them into it.
more recently i've done a ton of streaming on twitch, where i was a part of a non-osu! community, and i managed to get several people to play the game who are still playing to this day. i'd say maybe 15-20 people new. i've also got several people back into the game who used to play before.
in addition because i mostly play taiko, i've got a bunch of people who play other modes to show interest in taiko after watching my stream or talking to me. i think it's really cool, and of the people who are truly interested, some of them have been able to get pretty good at the game as well. one of them even passed me in rank and got very close to the top 200. c: