Should I include a clause similar to this in my website T&Cs? I can't see anything exactly equivalent in your standard documents.
"You retain all ownership rights in content posted on our site and relieve us of any and all liabilities that may result from your content. We take no responsibility, legal or otherwise, for your content."
This provision attempts to do several different things.
First it says "you retain all ownership rights in content posted on our site". This refers I think to intellectual property rights, specifically copyright. These rights will usually only be passed from one person to another by an express assignment, so arguably this part of the provision is otiose. Also, the text assumes that the user does in fact own the rights - that might not be the case. If you want to include something like this to give assurance to your users, I suggest a slight rewording:
"Nothing in these terms and conditions will constitute an assignment to us of any intellectual property rights in your content."
Next, "you ... relieve us of any and all liabilities that may result from your content". This looks like an exclusion of liability with respect to the user, but on a closer look the meaning is not very clear. For example, if the website operator uses the content in breach of the licence granted by the user, is the operator supposed to be liable to the user in those circumstances? If you take the exclusion seriously, then it would appear not. It is important that exclusions are clear because otherwise they may be ineffective.
Finally, "we take no responsibility, legal or otherwise, for your content". Again, I don't think this is terribly helpful. What is responsiblity in this context? Liability? Why the reference to non-legal responsiblities? In respect of liabiltiies to third parties, the document cannot have any effects here - and an exclusion of all liability would likely be ineffective.