I love the synergy of a long run -- when my mind and body find a groove and pace and stride for a decent amount of time. No matter how crummy the previous day was, this helps clear out the junk in my head. Problems don't disappear, but it helps me see them more objectively.
These runs are all too rare, but coveted the way I coveted a good nap or a great steak.
I hope to see a few of these this summer.