I read this was to be released late last year! I think it will be fantastic especially for the software developers. And people will be able to find all (most) the apps they need in one place like a library.
But will this mean less effort into the sexy product websites we see at the moment for OSX apps? I hope it doesnt make them redundant. Maybe this could be the future of the internet, where it just becomes a network of librarys. Facebook being another for example.
I'm glad they're bringing the kind of possibilities you see on the iPhone to the Mac. I love using my main computer -- it represents 90% of my time... so naturally I want the best world to be there too.
Even if that means we'll see a lot of crap, we'll also see AMAZING ideas like the flipboard app, more casual games for your family, and magazine in one centralized area that promotes great UI!
Twitter for mac, although it's being looked down on as a replacement for Tweetie 2, is beautiful and functions amazingly well! I love how it uses the Stream API so tweets come through almost instantly!