The switch to touch screen and adverts all over your library & store is really jarring. So much so that my tech friends now just buy second hand kindle 4s when their old ones break.
It's possible that library lock in will stop them migrating away from kindles when the supply of kindle v4s runs out but not I think certain.
Some purists would prefer to avoid buying DRM'd products in the first place (and I do when I have an alternative), but this is "second best" to me - I'll tolerate easily breakable DRM, but not one I can't remove.
The upside is reduced lock-in - it may affect usability (the Kindle app is still the best reader app I've used for Android as well - if anyone has recommendations for any actually usable ebook reader Android apps I'm all ears) but I know I can read all my books on any device, using free/open apps.
The only real benefit of kindle is the library selection and prices. The ereader software itself is mediocre.