MarathonGuide.com, my favorite site to "shop" for a marathon has just released it's annual report. Due to copyright restrictions, I won't copy/paste it here so here's the link.
Some interesting topics include:
1. Marathon finishers (overall demographics, male vs. female, history since 2000)
2. 2007 Largest USA Marathons (including 2006 and growth/shrink percentage...very interesting!)
3. 2007 USA Inaugural Marathons
4. 2007 Age Group Breakdown (age demographics, fastest age groups, largest age groups
5. 2007 Marathon Finishing Times (by gender)