I was on a date when I saw Arrietty, and we were the only people in the theatre. Which was a bit surprising, as it was is in Queens which is like Asian-central (my date was a Chinese girl... who later turned out to be crazy).
Princess Mononoke (my first Ghibli flick) was at the local LI movie theatre that shows lots of indie flicks and I remember it getting a fair amount of people. Since that theatre tends to draw crowds who go to lots of different movies (they sell season passes and such). Ditto for when I saw Howl's at that same theatre. Spirited Away was at a regular theatre in Buffalo and I don't really remember how crowded it was, I convinced all my college friends to go and surprisingly they all liked it, even though most of them's only prior anime exposure had been DBZ.