(Note to porphyrin: it is blue.)
My philosophy of this thing is that I do not want to use it to replace physical books I would actually buy. So what I'm reading on it right now is...my own book. (One of my old manuscripts, I mean.) If I'm critiquing a manuscript for those of you for whom I do that, it'll probably be on my Kindle rather than in a 3-ring binder. Ideally this will mean faster crits.
I'm also interested in the sorts of free things that are open source, so if any of you have recommendations for specific works or sites for getting free old books in Kindle format, please do say. Again, I will continue to do my book buying in physical form for stuff that's available in physical form. What I want on my Kindle is Project Gutenberg type stuff, although Baen's Free Library stuff is also a good category of thing to have. Oh, and the last category is stuff that's only available in e-book format. All good recs to have.