It's funny, I was thinking about this yesterday after I practiced. I may have beaten my high run, but wasn't counting, so I couldn't tell. I was thinking that if I had been counting I may not have run as many. For me personally, I feel that if I'm not yet capable of running 100 balls, I don't really care what the run is. Sounds snooty, I know.
But what I may start counting are the misses when I practice. I like the attitude that there's no reason to miss if you play smart, so the 5th ball or the 500th ball are approached and pocketed the exact same way. Thinking like that should take the pressure off of a target number. You're either playing smart straight pool or you're not. It all should look very routine and boring no matter where you happen to be in a run. When you look at a run like Mike Sigel's 150-and-out against Mike Zuglan, you realize that high runs can be composed of easy shots. He rarely puts himself in traps where he has to come up with a trick shot. This tells me that with enough knowledge and cueball control I can have similarly high runs.
That said, if I find myself routinely not missing for a half hour or so, I may start to keep track of my runs, because I'll then know that I've acquired the knowledge to be able to run a hundred or more. I really just want to keep learning and getting better. If I run a 100, I won't be looking to run 150. I'll be looking for new knowledge that will Allow me to run 150.