Some people are thrill-seekers—I think I'm a numbers-seeker. One of the funnest parts of my marathon training was that each of the long runs was the farthest I'd ever run, and that I kept having that kind of personal-best success every week or two. (And the Nike+ system didn't hurt, when Lance Armstrong or Paula Radcliffe would come on my headphones and let me know that I'd just set a new personal distance record.)
This year I'm having that same success with my swim training. I just did 1100m this morning and that's the farthest I've ever swum. Ever! And this last weekend I did 900m in the lake, which is the farthest open water swim I've ever done. (As well as being my second real open water swim.)
I suppose I'll eventually run out of things to keep getting better at (because, no, I'm not doing ultra-marathons or anything) but I'm already thinking ahead to next year and thinking that a bike century might be a nice goal…