When my Twitter followers started telling me last night that Kindle for iPhone was out, I downloaded the free App immediately. I have been using a (real) Kindle for months, and absolutely love the experience and flexibility it provides. Having the ability to access all that content with the device that's almost always in my pocket sounded fantastic. And it is... within the limitations of the iPhone itself.

The Good Parts

• The Kindle App for iPhone is free. Just head on over to the iTunes App store, download it, and you're good to go.
• It syncs with your existing Amazon/Kindle account. Books you have already purchased for your Kindle will be automatically available for your iPhone once you authenticate with your Amazon account.
• WhisperSync takes it one step further. If you've read a bit of a book on your iPhone and sync it back to Amazon, then the next time you pick up and sync your Kindle it will know exactly where you left off. I can totally see myself using this: reading most of the time on the Kindle, but if I get stuck in a doctor's office waiting room, I can sync up with my iPhone and read a few pages while I wait my turn. Fantastic!

The Drawbacks

• You're reading on the backlit iPhone screen. Sure, this is good enough for light sessions, but I can't see myself reading for an hour or two on an airplane while staring at the iPhone's screen. The Kindle devices (both original and second generation) instead use e-Ink, which allows for a much more natural reading experience that comes very close to reading real paper on a real book. This is key.
• No newpapers/magazines/blogs available on iPhone. At times I have subscribed to newspapers via the Kindle and have very much enjoyed the experience of reading them electronically there. They come in magically every day and the Kindle provides for a very smooth navigation experience that is far better than reading the paper-based alternative. This is exactly the type of bite-sized content I would like to read on the iPhone, but the Kindle app does not support this (yet?). Sure, I can use the Web browser or other apps to access analogous information, but I would probably prefer it in the Kindle app.
• The Kindle Store for iPhone. It doesn't exist. In order to buy books for the iPhone you either have to use your Kindle or your Web browser on your Mac or PC. Sure, you can use Safari on the iPhone, too, but there's no "special" iPhone-formatted interface, and navigating Amazon's standard Web interface is an exercise in patience (and fat-fingering!). Even Amazon's store app for the iPhone doesn't allow for digital downloads, so this solution needs to be flushed out better.
• Battery Life. Reading with that backlit screen for any long-period of time is a huge drain on the iPhone's already-short battery life.

The Kindle's reading interface is actually quite smooth, and transitioning from page-to-page is seamless with a swipe of the thumb or finger (perhaps the accelerometer can be used in future versions?)

I wouldn't want to navigate this store on my iPhone, would you?

Gateway Drug

Honestly, I see the Kindle iPhone app as either a great accessory for Kindle owners or a fantastic marketing move by Amazon to kindle the appetites of would-be, er, Kindle buyers (sorry, the pun was too good to pass up!), getting them that much closer to that critical point-of-purchase decision. But it is cool, and for free it's a no-brainer.