Well, the guy from St. Clair software has a beef with it b/c his software (Default Folder X) is a system pref pane, and it supports open meta (which Apple could break at any minute). I use DFX, and I really like it. That said, I do a bit more with my computer than most folks I know.
Those of us here on MR will continue to be able to find software that suits our needs, and folks who use the app store will do that. I can't imagine the average user having much need for something like Transmit from Panic, but I'd be surprised if it wasn't there. On the other hand, the guy who does Bean (a lightweight word processor) could easily put his stuff up there since just about everyone who sits down at a computer will do some kind of word processing/text editing at some point.
I'm not a developer at all, and I think of myself as more than a basic user. I'm really excited to see what the Mac App Store will offer, and I also hope that devs are able to continue to make their products available elsewhere, too.