You did.  They also said at the same time they have lots of backups which can and often does include deleted or edited posts.  They said this just after the silk road stuff blew up because people were panic deleting posts or editing them to obscure the content hoping to avoid criminal prosecution.

However posts here from unaffiliated people would generally not be admissible.  Evidence should be from the original source as a general rule.  

This is somewhat different from the hearsay rule which is probably what some readers of this thread would be thinking of.  That rule says that a 3rd party cannot say what they were told was said (eg "Alice told me that Bob said ...") generally that is because its not the original evidence but not exclusively because of that.  However if you are part of a forum you might be able ot testify to what you personally observed as a participant in that conversation, there are exceptions to the original source rule and ultimately it would come down to the judge and the arguments the lawyers present (if it even comes to that).