(I know I said I wasn't going to play any more, but sometimes I can't help myself.) This thread should have been split at some point in the past because there are really two discussions going on here:
One is about DRM. Not whether it's effective, there seems consensus that it is not, but - as per the title of the thread - whether it is good or bad for the author and/or publisher. I suspect the reality is that DRM, even in its current form, does serve a purpose: it does stop a (large?) portion of the casual forms of sharing that would otherwise take place without anyone even thinking about copyright; many people just don't know nor care. Yes it can be unfair to the reader, but as so often happens in such situations, it is hard to get the provider to worry about issues that don't effect them directly.
As to the overall effect of DRM on the author in terms of revenue? I am not in a position to say, I'm guessing that the publishers have a better idea than I do (I certainly hope so). The anecdotal evidence of a few people here suggesting that they'll pay for non-DRM books, but they'll only ever obtain pirated versions of DRM books (despite how easily they tell us DRM can be removed) I do not find very convincing, in fact it sounds quite contrary (a self-deception used to justify not paying for a book, what other explanation fits?).
The other discussion is about piracy. This applies as much to DRM protected books as it does to non-DRM protected, the main difference between the two situations was noted above and gives DRM its reason for continued existence. (You could even argue that DRM is there for the readers benefit, protecting them from accidentally becoming pirates... but I don't really expect you to swallow that one.
) As previously noted the term "piracy" is pretty loose, I prefer to use it only for the illegal distributors, rather than recipients. (Like the difference between thieves and receivers of stolen goods.)
In that light, listening to the various justifications that people offer for piracy reminds me of that Simpsons episode where Fat Tony justifies cigarette smuggling. (Paraphrased: "Is it a crime to steal a loaf of bread to feed your starving family? No sir. Now what if they would prefer something other than bread, say, cigarettes - would that be a crime? No sir. And what if, instead of giving them away, you sell them for a price that's practically giving them away, would that be a crime? Hell no!")