I just got the email from Amazon PR.
Kindle for PC features Amazonís Whispersync technology that automatically saves and synchronizes bookmarks and last page read across devices. Whether you read Kindle books on a Kindle, Kindle DX, or one of the free Kindle applications, you can always have your reading with you and never lose your place. With Kindle for PC, you can read some on your PC, read some on your Kindle, and always pick up right where you left off. Whispersync helped make the Kindle for iPhone application the most popular books app in the Apple App Store.
"Kindle for PC is the perfect companion application for folks who own a Kindle or Kindle DX," said Ian Freed, Vice President, Amazon Kindle. "Kindle for PC is also a great way for people around the world to read the most popular books of today even if they donít yet have a Kindle."
It hasn't been released yet, but you can check on the status of the software here: