Dan, sorry to burst the bubble here, but in my opinion a user should ALWAYS be able to go back and edit a post. The pros (of realizing you didn't say something correctly, or adding info to your original post, or editing and saying that what you originally said was found to be wrong) far outweighs the cons (of a user deleting his post and then saying he never said such a thing...)
Just my 2 cents. Although I have the power to change it, and it doesn't affect me anyway, I'll let you decide.
Stece2, with this one, I'm with you.