Hi, I have several times been annoyed by the fact that after a certain time you can no longer edit your post. My suggestion: Enable editing at all time but enforce a field of "reason of editing" that shows up on the thread.
Hmm, I can see the reason for that And by thinking a bit about it I can see that that is more important then "my" reason. But you have some examples like latehorn making a new thread each time he has to update his dir list, well well. EDIT: Red rep for a suggestion, ok ....
The bad hats/scammers are not supposed to go back and edit posts of agreements or take away evidences etc. If you cannot edit it is more safe kind of as you can go back and see what was really written and nobody can take it away.
When you make something that'll be updated over and over, the best thing to do it post it off site and link to it, like for example the CO-OP, AdSense and YPN FAQs. Odds are you stop being able to edit posts so people can't change selling info like price. err I think I better increase the price I want to sell that...!!! gah!! Won't let me edit!!