Currently, the top titles on the iTunes-style application include Angry Birds for $4.99 (50% off for a limited time), Chopper 2 for $1 (80% off for a limited time), and Flight Control HD for $4.99. A total of nearly 100 games are listed as of the time of this writing. Also, much like iTunes, the Mac App Store will notify users of updates to their purchased applications and make updating extremely easy. Purchases are tied to a user's Apple ID, which is already used to buy items from the iTunes store.
Whether you'll get as much use out of the application as you do the Mac version of Steam is up to you, but it's good to see a little more organization (and a detailed database) added to Mac's numerous non-gaming applications.