My Dad got a Sony reader for Mum for Christmas. E-ink, reads a number of formats including PDF and ePub, standard micro-USB and appears as mass-storage. Simple, easy, yes? And then he tried to buy an ebook from an online retailer. But he runs Linux.
It seems most DRM on eBooks is Adobe's Digital Edition. This currently requires Windows, as they won't release a Linux version (it was announced, and then withdrawn to considerable criticism). I've heard noises it works under Wine, but I couldn't inflict that on Dad without testing it myself. It is also possible for the publisher to encrypt the ePub file with DE such that it only works with your reader.
They gave up and used my sister's PC which runs Vista as she must use Adobe graphic products (otherwise she'd try Linux :-). The Sony library app is actually rather good; the Angus & Robertson one is atrocious and should never have been released. Rather shortsightedly, A&R's website also had *no* information about non-Windows platforms; you may well find this problem on other retailers. I have since found a few sites that offer DRM-free ePubs and I bookmarked them for Dad.
I suspect that the ebook publishing industry is going to find itself in the same pickle as the music publishers within a few short years: and the masses will make them re-think DRM.
Wade.