I'm sorry, re-reading my comment it came out a bit pompous which was not the intent. I used to do them a LOT and I really mean a lot! They are one of my favorite exercises, but after a while they just aren't as challenging as they once were. And seriously its one of the easiest exercises to get good at because you don't need anything but yourself and a willingness to get weird stares and comments!
Do 3 per leg every hour or so for about a month and by the end of the month you will be doing give or take 20 per leg.
I'm good at 5 things:
1. Making myself look like an ass!
2. Making myself sound like an ass!
3. Doing Weird Workouts!
4. Shooting People! (A skill thankfully that is used infrequently!)
5. Teaching Skills 3 and 4 to others!
I have no social life, and I'm ok with that!