Two developments have made me consider purchasing a monitor:

(1) my old running watch died

(2) after 6 relatively easy-paced marathons since March, I’d like to begin challenging the clock and a heart rate monitor seems like a good way to make sure I’m pushing myself while training.

Any thoughts on monitors?

I got the Polar F11 Four months ago and it's changed my workouts. Not only have I programmed specific targets for myself, but the ability to track your workout levels over the course of time keeps you honest.... And it's very motivating! Also quite illuminating: I never realized to such an extent that when you reach your anarobic peak, your breathing slows and deepens, but your heartbeat keeps climbing and climbing... I reommend it.

Thanks, StonyKill. I went with the Polar RS100 and have been happy. It's been helpful for me to get a feel for my 60-70% heart rate range for running ultras (so far so good -- completed the Jay 30 miler in July and the Dances with Dirt 50 miler in September).

I've been running conservatively so far -- I'm going to try to push it closer to the 70% level for the JFK 50 miler in November.

Thanks again for the advice,
Eric