Looking over Blogdex, I found this interesting editorial piece from Roger Ebert that points out the differences between 'horizontal' and 'vertical' prayer. Obviously, I find all this talking to your invisible friend up in the sky generally amusing, but Ebert has some important points to make:

This is really an argument between two kinds of prayer--vertical and horizontal. I don't have the slightest problem with vertical prayer. It is horizontal prayer that frightens me. Vertical prayer is private, directed upward toward heaven. It need not be spoken aloud, because God is a spirit and has no ears. Horizontal prayer must always be audible, because its purpose is not to be heard by God, but to be heard by fellow men standing within earshot.

As Bartcop has regularly pointed out over the years, whenever this subject comes up - it's impossible to stop someone from praying, if they actually want to pray. If, however, they wish to loudly proclaim their faith and start inveigling others to join with them, that's a different matter, but some people choose to wilfully ignore that. Or, as someone reputedly said 2000 years ago:

And when thou prayest, thou shalt not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward. But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly. (Matthew 6: 5-6 - found thanks to the Skeptics Annotated Bible)