@ben I, too, have a Kobo and am *mostly* happy with it. The device (a Libra) works nicely, is reasonably open (you can put apps like KOReader on it, for example), and it works well with Calibre, easily enabling all of the useful things that a suitably extended Calibre can do for you.
My biggest complaint is that, after a few years, the battery is failing, and the device was not made with repairs in mind. The new Libra they offer now claims to have addressed that, making battery repairs feasible.