You might not have noticed, but your Kindle for Mac has probably stopped syncing with Amazon since updating to OS X Lion, even if you have the most recent Kindle update. Even re-downloading it from Amazon doesn’t solve the problem.
Here’s how to fix it:
1. Delete Kindle.app from your Applications folder (don’t panic! This doesn’t delete your purchases or any added files, just the app).
2. Drag the Kindle icon off the Dock and release it anywhere on the desktop.
2. Click on the App Store icon on the Dock, search for Kindle and install.
3. Don’t forget to make a new icon for your Dock by dragging the Kindle app over from Finder.
That’s it! Syncing restored, but be aware that the App store version of Kindle is an old build. The latest Kindle build with support for Collections won’t work with Lion yet. For that, we’ll all have to wait on the developers…