Thanks everyone for your comments and perspective on the whole runner's "high" thing. Thinking about what Jeff L and jeff (from Alaska) have said it occurred to me that there are really 2 kinds of experiences I'm thinking about when I think of having experienced the runner's "high".
Primarily I'm thinking about the "in the zone" or somewhat euphoric condition that typically happens in the middle of a race or long/hard tempo run. Where it feels like everything is just clicking perfectly and the running seems effortless for a period of time.
But then there is the less euphoric but I think equally satisfying feeling that comes during slow, easy runs, typically for me in the hills or somewhere scenic, where you just have a feeling and peace and serenity and a feeling of being "at one with the universe" or whatever. I remember last December running with Kim and we got caught in a snowstorm with huge flakes and we started staring up into the falling snow (
http://tom.fastrunningblog.com/blog--Had-planned-to-go-run-this-morning-wit/12-08-2007.html). We both got caught up in this overwhelming feeling that is just really hard to describe. Going back and reading my entry it almost sounds corny, but at the time it was just a really indescribable, spiritual type of experience.
So I guess then you've got the hard effort, euphoric type runner's high that is in some ways similar to a drug-induced "high", but then you've also got the peaceful, serene type experience that is more of a spiritual thing. Of course I think they're both awesome feelings, I agree with you jeff that the longer you've run it seems these "highs" become less frequent. But also to paraphrase what you were saying.....we all just like to run, and that is good enough reward in and of itself. Every run really IS a great run, with or without the high.
And thanks Jeff L for reminding me how lucky we are out here to have beautiful mountains, canyons and trails to run on within minutes from our homes.