Having been bitten twice by retrospective removal of reading permission on ebooks (MS Reader and Fictionwise), I now strip the DRM from all ebooks I purchase regardless - as Stallman says, if I buy a book, then I own it and can do more or less what I like with it...
The other, even more pernicious problem though, is the arbitrary (to the customer anyway) restriction of the availability of ebooks. I have an extensive collection of certain authors in paper form (Eg Terry Brooks) - I have been to all the major ebook publishers and attempted to purchase the ebook versions to replace the paper ones. In the last two or three years this has become almost impossible, because - living as I do in that hot-bed of communist, right-wing, islamist reactionary terrorism, the UK, I am not allowed to buy electronic copies of books that are freely available in printed form in my local bookshop (I note however, that Iran, Iraq and Korea are all allowed to purchase copies!)
So, despite my having offered to pay a second time for these books, and hence support both the publisher and author, I am unable to, so I have had to find other ways to replace copies of printed books I already own. How can this possibly benefit either the publishers or the authors? I have debated this with Barnes and Noble / Fictionwise / Mobi in the past, but they seem powerless to influence the publishers that impose these restrictions, which are in fact more onerous than those placed on DVDs and Blu-Ray!