I didn't use QuArk, but I did use (and bought a copy of) Qoole[1]. I built several Quake2 levels some of which I released out into the wild:
http://www.jaruzel.com/apps/quake2/
I recently tried to get Qoole back up and running, but it really hasn't aged well. Making levels in it now, seems like way too much hard work.
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[1] Qoole Screenshot: http://www.cs-h1.do.am/_ld/2/50880145.jpg