I recently responded to an excellent post by Chris Saad (a fellow board member of the DataPortability Organization). He basically layed out scenarious for hosting, posting, and monitoring comments posted to websites.
His full post is at: Rich , Interactive Features for your siteFinding balance in the force
The rights conveyed depend on the context. If I agree to post to a public forum, then I should be aware that my comments may be copied and propagated all over the place – and there’s not much anyone can do about it. I’m ok with this because I knew going in that is was a public forum. You, the site owner, do not have the right to modify my content unless I say you can. You do have the right to delete it in its entirety (revoking the invitation to post in the first place).
On the other hand, if I post something when you tell me that the venue is non-public or limited in scope, then I have every expectation that you will honor that representation. But you still can’t change my stuff unless I specifically grant you permission (BTW, you may get that permission as part of the TOS provided before I post).
An important variant on this theme is related to mature and potentially objectionable content – again dictated by context. There is no world-wide sensor (thankfully) and there is no clear standard for mature or objectionable content. Once again, relationship must be dictated by conveyance, that is: you get to post on my site provided you agree to a, b, and c. And, you can be comfortable in posting on my site because I represent back to to you x, y, and z.
From a technology implementation standpoint (and I am quite familiar with JS-Kit’s awesome products, having dealt with them previously through Zude), the real challenge/opportunity is all about the flexibility of dealing with all of these scenarios without encumbering the product or confusing the user.