Two years ago, I ran my first marathon, the White Rock Marathon in Dallas. Last month, I ran it again. In between the two, I ran a number of other races, a grand total of 11 races of marathon distance or greater in a span of just under 2 years, plus a couple of ultras in which I DNF'd (after 19 and 25 miles respectively) and a few shorter races. On the one hand, that sounds like a lot of running. On the other hand, during that time I've met a number of runners who run marathons almost every weekend, or run back-to-back ultras.
I don't know where my perfect balance is. Sometimes I think I recover well, but sometimes not. It took me a while to feel back to normal after White Rock. I'd love to be one of those guys who can run a marathon on Saturday, then another one on Sunday, and then run a 50 mile trail run on Saturday. Or who can finish 4 mountain 100 milers in one season. At this point, I'm not one of those guys. But I think I can get there.