For the record, the people who pray because they think they'll be going to hell if they don't are doing it for the wrong reason. There are two reasons not to be religious; they were described to me once as the path of the thief and the path of the coward. The thief believes that by believing in God he can gain something for himself -- this is similar to a lot of people I know who believe that since they believe in God, It is obligated to forgive them or grant them wishes or whatever. The problem here is that these dudes believe they have control over God, and thinking you're more powerful than God is a big no-no.
The coward believes because he thinks that he'll go to Hell if he doesn't. Simply put, he's still in the religion for his own interests. I think I have more of a problem with this than I do the thief, because for one thing I disagree with the notion that anyone who doesn't believe in a thing of infinite grace and mercy will be sent to hell by that thing because it doesn't like being ignored, and for another it's a horrible way to convert people. Unfortunately, it's also a very popular way of converting people at the moment. Then again, I disagree with the notion of converting people in general, so...
Anyway, prayer isn't for God so much as it's for you. The way I see it, It doesn't have any special need for a pat on the back, but It does tell us to play nice. It's a way of keeping you on the straight and narrow by reminding you that Big Juju gunna smack you if you do wrong. You best watch yo'self. Muslims pray five times a day, the assumption being that if you've just prayed, you're not going to go out and murder anyone or anything like that. Of course, that doesn't work if you assume the dude you're praying to wants you to kill people... :x