I haven't bought any ebooks. I have read some that were available for free and some that I received as review copies, and I feel there's a lack of quality control in the industry as a whole. Reputable publishers put out quality material, but vanity publishers and self-publishing efforts often sell sub-standard products. I am especially wary of ebooks on topics relating to making money online, whether marketing or selling articles or any other work-from-home plan, because I've seen too many such books that were put out by people who had essentially failed in the subject matter they claim to teach and turned to selling hope to the unwary instead. And those books, in my limited experience, often turn out to be nothing more than a collection of blog posts or other freely available materials, repackaged for sale.
Note: Obviously I'm talking about ebook-only products here, not books that are published in both ebook and print formats. I've purchased a lot of those. My Nook has saved me from buying at least two more bookshelves for my office.