I'll add an anecdote to the (small) pile.
Sidebar: I won't buy e-books with DRM that cannot be stripped out relatively easily. I do buy the books I read, but I'm not interested in losing access to them in the future because technology shifts or a company goes out of business.
I've bought perhaps thirty to forty books from Kobo in the last three-ish years. In that same time I've bought two from Amazon, two from Sony, and one from B&N.