I've written about this with greater sophistication elsewhere in "Sitting."

I'm not fond of praying or having people tell me they will pray for something. The reality of this action became clear to me while studying Buddhism. 

When a Buddhist meditates, he/she is usually calming the mind in order to detach it from desire. Principal amongst these desires is the desire to exist. The Buddhist seeks liberation from the self, which is a desire to exist. From the Pali, anatta is no self, no soul. In part, meditation is the embrace and full realization of no self.

Prayer is inherently acquisitive. The person praying is asking for something from something that can grant it. The impulse is diametrically opposite the Buddhist. The "me" asks the "something in whose image I am made" to grant me a wish. The vanity is that you have a "self" that can ask. The hubris is that your "self" is made in the image of something that can grant favors.

The Buddhist does not pray because there is nothing out there to pray to. Also, since Buddhism is about freedom from desire, begging an omnipotent being for favors would be inherently contradictory.