From P.Z. Myers at Pharyngula:

Top Ten Reasons Religion is Like Pornography

1. It has been practiced for all of human history, in all cultures
2. It exploits perfectly natural, even commendable, impulses
3. Its virtues are debatable, its proponents fanatical
4. People love it, but can’t give a rational reason for it
5. Objectifies and degrades women even when it worships them
6. You want to wash up after shaking hands with any of its leaders
7. The costumes are outrageous, the performances silly, the plots unbelievable
8. There’s nothing wrong with enjoying it, but it’s nothing to be proud of, either
9. It is not a sound basis for public policy, government, or international relations
10. Its stars are totally fake

For more context and discussion of this list (including suggested additions and criticism) visit Pharyngula.

UPDATE (October 4, 2006): The slides for the talk in which this list was given–about why scientists should oppose religion–may be found here.