ArsTechnica does a hands-on of the Mac App Store app:
The store works pretty much as you would expect, especially if you’ve downloaded apps through the iOS App Store. If you’re using the MAS to browse, you may find yourself annoyed that there are no breadcrumbs across the top like there is in the normal version of iTunes; you just have to remember where you’ve been if you decide to hit the back button a few times.
It feels lighter because there’s less going on onscreen.
Another complaint that some early experimenters have had is that there’s no built-in uninstall functionality within the MAS—when you install an app on your Mac, you have to get rid of it the old-fashioned way (by moving it to the trash, or by using a third-party uninstall tool) if you don’t want it anymore.
Why would a user want to buy from the Mac App Store?
It’s a place to find (mostly) good quality software, and it’s a centralized place to browse for apps you haven’t even heard of yet. The discovery potential is huge, while simultaneously offering a much more organized experience than surfing the Web looking for software. The software buying (and updating) experience has now been simplified significantly, which is appealing to people who don’t have the time, energy, or skills to do all of those things on their own. Because of this, people like our parents (or anyone who expresses anxiety at the prospect of installing things and “breaking” their machines) may finally be able to let their guard down when it comes to installing software.