Personally I think the mac app store is a great idea (if very similar to the app store for iOS):
1. Allows me to see reviews and screen shots - to decide if I want to buy this software or make another choice. Also to see if I should skip this update or not.
2. I could piece meal my purchases. I need new imovie, but have no need for a newer garage band, or iweb (since they don't seem to update that). Also, I only use the basics in iphoto - so I would not upgrade in a long time. I use pages often, but I never use numbers (I use excel due to the windows world). and for presentations, I am looking at buying ProPresenter.
http://www.renewedvision.com/
3. Would be great if I could backup all my software (mac and iOS) at the same time I do my itunes backups. this way, no remembering to have to make separate CD's of each software. I just rely on my time machine and then when I do my monthly backup of itunes to DVD(s).
4. Since it was purchased from the mac app store, and thus registered to the user/machine that did the download. Serial numbers would become obsolete. No need to write down serial numbers in a log book, or on the CD (especially since we are moving from a CD world to a download world).
5. Updates would become automatic (like the way iOS apps update).
6. Since it would be stored in iTunes, with your Apple ID would be nice if all software became family-paks. This would be 1 standard price point, and on multiple macs I own (like I do with my iphone and ipad).
7. Syncing data between devices would then hopefully become less trivial (ie like ibooks and several other apps). Just load it into itunes, sync and viola - it is now on my phone, and ipad just by plugging it in. Itunes would need a way to push to all your registered macs (using your apple ID).
8. And let's not forget... No more dedicating a drawer in the file cabinet just for the boxes the software came in. Yes I save the boxes, because when I upgrade - I give the older versions to other people who really do not need the newest and greatest, or if they cannot afford the software. Plus I also can just easily look at the box than flip through a book of CD's when I need to re-install (rarely - that mostly happens on the 1 Windows laptop I have).
9. Unless developers become greedy pigs, software prices could go down; as they will not have to build-in the price for CD's, print, boxes, shipping to a distributor or directly to the store, returns for damaged shipments or if it does not sell and the distributor returns it.