I hold the copyright in the answer I'm posting as I type right now. If you copy and paste it elsewhere (even if you acknowledge the source), you're breaching my copyright. Even if you simply print out this answer for your own use, you're technically breaching my copyright. (No, I'm going to sue you; I'm just trying to make my point clear!).
The creator of any work holds the copyright in respect of that work unless
(a) they're creating that work in the course in their employment (in which case the employer holds the copyright) ; or
(b) they assign the copyright to someone else. (e.g. the Answerbank could make it a condition of using this site that all contributors assign the copyright in their posts to AB).
Copyright in any work exists automatically. There's no need for anyone to write 'this work is copyright' or put a � mark alongside it. Every post on the internet is automatically copyrighted by the person making that post.
So (theoretically at least), if you take '1000 crazy stories' from the internet, you'll require the permission of all 1000 originators of the original posts. In practice, many of the people posting would either not know about your reproduction of their posts or not be bothered about it. However, it's extremely unlikely that any publisher would accept your book, simply because their legal department would warn them about potential legal challenges regarding copyright.
Chris