probably around 20-30 weighing at 155lbs...
in my prime, i was doing sets of 30 reps at a nice slow steady pace. never tried to max out fast but i reached around 42 (in the 40s for sure) once pumping them out as fast as i could. dips were always my last "weight" exercise on my old chest and tris days routine before abs so my triceps were pretty worn out by the time i hit the dips workout. pretty sure i could have don a lot more. i don't lift a lot of weights anymore though. if i have time, i'd rather box.
i love doing dips. it was one of my favorite workouts besides benching.