Re: Kobo keeps you free
"I went for the Kobo because they don't seem to cage you nearly as tightly."
Although a Kindle user myself, that's pretty much what I took away from this article too. Amazon are an e-book seller who will sell you a device to access their Library. Kobo are an e-book device seller who have a library but are happy for you to buy/borrow from elsewhere, DRM not withstanding.
Of course, either is ok when you have a PC and calibre, but for the "appliance" market they are differentiated by their attitudes to 3rd party book suppliers.