There actually have been scientific studies done on the therapeutic benefits of prayers in hospital settings which show improved recovery rates and more positive overall emotional states for surgical patients who prayed versus ones who didn't, but unfortunately I can't link to them as they're in scientific journals which require membership in university libraries. I've run into this problem before in backing up claims I've made (and would like to make) in various online debates.
Anyway, here's the gist of the argument for prayer: It's not that the deity prayed to necessarily reaches down and intercedes directly, it's that the individual doing the praying or spiritual meditation or scrying or what-have-you benefits from calming themselves and focussing their minds. The interactions between mind and body are still very poorly understood, and it's thought that the act of prayer performed by someone who truly believes provides an emotional state which is more conducive to the healing process.
Be considerate to others or I will bite your torso and give you a disease!