Kindle's biggest strength?Platform ubiquity. Even more so after this Kindle for Mac update that lets you add and edit notes and highlight passages, syncing everything across all Kindle apps and devices.
That cross-platform functionality—through Amazon's Whispersync technology—is the standout new function, but you'll also now be able to search within a book, and use a multi-column reading mode. There's also a slightly tweaked user interface.
Something about reading books on a laptop still doesn't have the appeal for me that a dedicated ebook reader or iPad does, but it's great to have as an option. I'd be a lot more inclined to take notes, in particular, with a full keyboard handy. You can pick up the update free here: [Kindle for Mac via Macworld]