If you took, say, a Harry Potter e-book, typed it out word for word and printed it you still couldn't sell it as your own. It'd just be a colossal waste of time. Whenever you copy something of note it's always best to ask the author first, however on forums, unless specifically noted, there is no expectation of protection of rights - you're releasing what you type into the public domain essentially. You could still take legal action if your stuff is copied but it's unlikely to get very far. Wikis often have disclaimers relating to variants of the GNU (/FSF) GPL, so that any work submitted may be copied and used without explicit permission under the terms of that license - assumin that the person owns the rights to the work they are submitting.