While Amazon hasn’t said anything about it yet, Kindle Cloud Reader is already live. It’s a web-based version of their Kindle eBook reader app. It allows you to read your books from the cloud or to download your books for offline reading thanks to the magic of HTML 5 (or a Chrome browser extension). It looks and works great.
Amazon says that the app officially supports Chrome and Safari. This means it works on PCs, Macs, Linux, and even Chromebooks. This also means that it works on the iPad.