Not as awful as other reviewers make it out to be. Still, some serious shortcomings. Lacks the functionality of the iPhone app. On the other hand, the automatic syncing is nice.
Oh, and to answer the snarky question about why someone would ever want to read on a laptop, I have two responses: 1) Sometimes, you might have a little break time at your computer when you can read, the sync feature means you can pickup from whereever you left off and 2) the Macbook Air is lighter, more comfortable (can rest while reading) and far more versatile than and iPad.