Any aspects that are annoying or unsatisfactory. Whether the kinds of books we (JREF forumites) are likely to want to read are available.
Annoying things: I find the experimental internet option annoying and frustrating (Though, I know it's 'experimental'). I like speedy, and speedy it is not. I do still use it when I'm out and about and want to look up something on Wiki, but only after I've found a comfy chair and am prepared to sit a bit if you know what I mean. Even on 4+ bars, the browser rendering is slow.
I find cookbooks on Kindle to be somewhat annoying to read, that's just a personal thing, I guess some things I'll continue to prefer print for. I have a subscription to Reason magazine and Asimov's Science Fiction magazine through Kindle and find them easy to read and navigate. And I notice I'm more apt to read 'everything' rather than picking and choosing my favorite stuff, so I probably get more out of everything this way.
I'll give a few books that folks here may like, I know everyone runs the spectrum of interests here so I'll just throw out a few popular ones:
Voodoo Science by Robert Park
Snake Oil Science by R. Barker Bausell
Science Friction by Michael Shermer
The God Delusion by Richard Dawkins (as well as a few other Dawkins books)
God is Not Great by Christopher Hitchens (as well as a few other Hitchens books)
Death From the Skies! by Phil Plait
Stiff: The Curious Life of Human Cadavers by Mary Roach
For fiction:
Dexter books are all on Kindle
some Douglas Adams
Anathem and other Neal Stephenson works
Lots of Tween science fiction/fantasy making its way to Kindle, as well as a lot of older sci-fi.
The coolest thing is that you can, by design, share books between family members with Kindle if you link them on Amazon. So if I read the first Dexter book and my husband wants to also with his Kindle, we don't pay for it twice. I wish that worked with the magazines. =(
I dunno if they'll start charging for free stuff. I'll just hang in there and see, but I'd be willing to pay a little more than I am right now for the convenience factor.