I certainly prefer non-DRM books and will choose a copy from a non-DRM vendor (e.g. Smashwords) over the same title DRM-ed from Amazon, even if the formatting is kind of messed up.
But I don't automatically exclude DRM-ed books from consideration, if that's what's available and I really and truly want to buy a copy in e-book format.
However, in order for me to purchase the DRM-ed version, it would have to have a cheapness like unto dirt and I'd have to be able to strip whatever DRM was being used. Or completely unavailable through other means, including the darknet and affordable second-hand paper copies.
Or I'd just have to click the wrong button when downloading what I thought would be a sample from Amazon and have it go directly to my credit card so that I'd lose out on the currency conversion if I returned and refunded it.
Oh well. At least it's something I was more-or-less vaguely interested in, was cheaper on Amazon than anywhere else according to Inkmesh, and I've managed to read three free promo/library books from one of the authors at no cost to myself, so I don't mind so much if she finally gets paid for this one.
But you can bet I'll be more paranoid about the damn 1-click button and padding my account with gift certificates now.