I no longer by e-books unless that is the only medium in which a book were to exist. Instead, I now only buy physical copies of books.
The extreme lack of portability, lack of user-friendliness, lack of share-ability, and, put plainly, the hostility for the purchaser has driven me away from e-books as my default book format option. I’m fortunate that both the frequency of my book purchases and my income make shunning DRM an option for me, but I consider it my obligation to vote with my dollars in this way just like I vote with my dollars for sustainable, fair-trade, animal-friendly, vegan, ethical practices with virtually all of my other purchases: food, clothing, computer hardware, computer software, household appliances, lodging, etc.
I think the important thing to keep in mind is the idea of least harm. Even if one’s finances were to inevitably compel her to shop mostly at Wal-Mart, it is still possible to make small gestures in other ways, to ensure that some of one’s money goes to local retailers instead, for example, or at least another large company that isn’t as hostile to workers and citizens.