Reminds me, one cool feature with the freebie Wahoo Fitness app is it'll display continuously on my iPhone 4s unless I choose to turn off the display. It doesn't time out or go into power saver mode while Wahoo Fitness is running. It doesn't drain the battery too quickly but I usually plug in an external USB battery while I'm running Wahoo Fitness in continuous display mode. The characters are large enough to easily see with Wahoo Fitness -- not so with Strava or Cyclemeter on the smallish iPhone 4s.

But I don't run the display in continuous on mode very often. The speed always lags behind several seconds so it's not really useful as a speedometer. A cheap dedicated speedometer would be better.