In the USA at least, copyright is inherent, so all one has to do is include the notice, and even that is optional. The problem with copyright enforcement lies in the expense of it, which can very quickly add up to many tens of thousands of dollars, and then one has to prove "damages," which in the case of a work that’s been published for public reading at no cost, are rather difficult to prove, and can very quickly add enormous costs to a potential lawsuit, even if the work has been revised.

It’s also possible to copyright a portmanteaux of "collected works" and have the same benefit (if any) of individual copyright at less cost, as long as one doesn't miss the three-month "window" which can elapse between original publication and filing. The current fees are US$35 for on-line filing of a "single author, single work" application, US$55 if one doesn't fit into that narrow window, or US$85 if one uses paper. In practice, all that means is that if you plan to copyright two or more books in one quarter, one might save a bit in filing fees by doing two or more at a time.

At one time, there were supposed "statutory damages" that one could try for, but subsequent cases have whittled away at this to the point that it’s almost entirely left to the discretion of the judge, so the putative "damages" could be as little as US$200, which wouldn't cover the filing fees in many jurisdictions, much less the costs of the attorneys involved. To be sure, statutory damages are only available if one has registered one's copyright, but the potential benefit is rather iffy these days. In these days of "free" publication, it's fairly easy for a potential defendant to arrange "prior publication" and "innocent infringement" evidence on their own, since all it takes is a little planning. I’ve had my own books "ripped off," and my publisher decided not to pursue the matter, claiming that they were unlikely to recover expenses (the infringers were located in China and South America, where my books weren’t being sold in the first place) since they hadn't made the books available to anyone, so they could hardly claim that they lost any substantial sales, other perhaps than from people who would otherwise have jumped on an airplace and flown to the USA for the express purpose of buying my books. Golly, I thought there might have been at least a few, but there's that pesky requirement of proof.

http://en.wikipedia.org/wiki/Statutory_damages_for_copyright_infringement

One notes that the case referenced and then studied was brought by Capitol Records, and that with the amount of attorney time and other expenses involved in multiple appeals, they likely didn’t cover their costs in the final "award," which was very unlikely to have been paid. Almost by definition, unless your book was ripped off by a major publisher, most defendants will either fly the coop or declare bankruptcy.

On the other hand, money isn’t a terribly good reason to become an author:

http://www.thecreativepenn.com/2012/05/09/is-it-worth-being-an-author/

One can have almost all the fun and very little of the hassle by simply publishing in a forum like this one.

Just sayin'