Okay, so now we just saw the app running on an Acer tablet. Apparently it'll use an accelerometer to rotate pages, depending on the orientation of the tablet. It'll work on XP and Vista too.
Here's the full press release (thanks Dan!).
With Kindle for PC, readers can take advantage of the following features:
* Purchase, download, and read hundreds of thousands of books available in the Kindle Store * Access their entire library of previously purchased Kindle books stored on Amazon's servers for free * Choose from over 10 different font sizes and adjust words per line * Add and automatically synchronize bookmarks and last page read * View notes and highlights marked on Kindle and Kindle DX * Zoom in and out of text with a pinch of the fingers (Windows 7 users only) * Turn pages with a finger swipe (available in a future release for Windows 7 users)
Update: You can sign up here, to be notified when the download is ready.