Pedro, over at Way Of the Mind made an insightful post about the efficacy of prayer.
He points out (among other things) that if God cured/healed the sick who pray for it, then atheists would be noticeably sicker, and for longer, than the theistic population.
I hadn't really thought of it exactly that way before, so it was a useful insight (I pointed out in comments that atheists would never get a good parking spot, either, because they'd all be reserved for those people who pray for a parking spot).
[musing on... If prayer works, and you pray for a parking spot while children die of starvation ... what does that say about you? Then again, if God grants your request, while children die of starvation, what does that say about God?]