I already have people recruiting me for Boston 2010 as my new time gets me into Wave 1 for this and next year, 2011.
I've never had a baby but I can't stop feeling that running a marathon is a bit like being pregnant and giving birth. The training can be unpleasant (as I would assume carrying another human in your body is unpleasant at times), the week before the marathon you just want to run it and get it over with (you're about to deliver you just want to get it over with), and the actual running is grueling (as I safely assume giving birth is).
However, after the marathon (and birth) are over, you get the post marathon glory: soreness, a great time, maybe a new PR, and lots of photos to review. I think the post marathon is a bit easier than being a new parent but like many parents -you then decide to jump right back on to the marathon (or reproduction) wagon again. We seem to forget the hard stuff and grow to appreciate the results more....so we do it again....and again, and again!
The new goals are being devised as I type...