I got a Sony PR-505 last year and have yet to purchase a single ebook.
The DRM bothers me, but there are enough python scripts running around that will strip it out of the epub/pdf formats that it's not that much of a concern.
Price is why I don't buy them. While there are a handful of public domain books worth reading (opinion) the real content is only for sale.
I just flat-out refuse to pay 50% more for the same content in basically the same format that the publisher already has filed away somewhere. When do you think the last time that a major popular author wrote out a manuscript on a typewriter was? Or longhand? You know it's already in an electronic document format somewhere.
No printing, no binding, no shipping, no stocking, no returns. No fuel, no toxic waste from the paper making process, no toxins from the inks.
Yet I get to pay 50% more?