Being a runner and cyclist, I know both sides of this issue. Here are some rules for running on the W&OD/Custis:

1) While zoning out to an Ipod might make the time go by faster, if you don't hear an oncoming cyclist yelling "passing on your left" and you weave into his path, time spent in the hospital goes by very slowly. Keep the volume down, more as background music, so you can hear those around you.

2) While the path is not all that wide, as a runner you're not some wide-load truck -- stay to the far right side of your lane so that cyclists can pass on your left without having to occupy more than a few inches of the opposite lane.

3) While it's wonderful to hit the u-turn of your out and back jaunt, it's not wonderful to have your sternum hit by a cyclist cruising along at 20 mph. If you're doing an out and back run, do not simply stop and turn around in the middle of the path. Step off the path on your right, turn around and check that no one is approaching, then get back on the path and finish the second half of your run.

4) While it's always a friendly gesture to wave hello to people, when you hear a cyclist calling out "passing on your left", don't stick your arm out to the left -- unless you're hoping for a dislocated shoulder. To let him know you hear him, raise your hand above your head and wave a finger in recognition (I suppose even the middle one if you're so inclined -- if so you might want to consider some sort of anger management training or self-help books, but ultimately that's your deal), or just say "gotcha" or "thanks".

5) While a congested Beltway is a given, a congested bike path is not. When running in a group, limit it to double file so that a cyclist can actually pass on the left side.

6) While no one likes a nag, most people appreciate it when someone is trying to be an altruist. If you hear a cyclist alerting you that he is approaching but you give no sign of recognition, verbal or otherwise, understand that if he continues to signal his approach he isn't nagging, he is trying to make sure that in fact you are aware that he is about to pass you.

7) While Fido or Fluffy love going out for a stroll, they don't like getting thwacked by a bicycle. Keep your faithful companion on a leash and on your right side so that he doesn't wander into the oncoming lane. Ruff ruff!

Note that none of the above absolve a cyclist from having responsibilities on the path. If a bunch of runners are clogging the lanes rather than streaming out their group, he should still slow down while navigating around them. If he heads toward a blind curve, he should slow down and stay in his lane until through the curve. That said, just because some cyclists might be aholes, that doesn't mean runners shouldn't follow the simple rules laid out above.