Yes, single source. There's only Amazon. You want to convert any of your existing files (as you mentioned), you have to use their (Amazon's) conversion process. You're tied to Amazon, unlike the iPod, onto which you have always been able to put your own content without having to first send it to Apple.

With an iPod you can also buy music at any number of other vendors selling music. It so happens it's non-DRM of course.

At a minimum I would have liked to see native PDF support, such that you could convert your own documents to PDF and put them on the Kindle without Amazon as a middleman.

My point of complaining it's too expensive and wanting more go hand in hand. At the current price point I expect a lot more. At the current implementation level, I expect a much lower price point.

I really have no clue what Amazon's costs are, but I suspect they're no where near what the retail price of the Kindle is. I have a feeling there's a (very) large markup. But that aside, my complaints aren't that a company shouldn't try to make as much money as possible. It's that I don't feel it's a decent value proposition at the current price when taken in the context of the current state of technology (and other not-like but capable multi-use products).