As for developers? For more than half of 2009, the App Store paid for my rent and cell phone bill. It helped me move across the country to the west coast. This was huge for me. I barely had to do much more than write code, design UI, and ship things. A huge chunk of the business of actually selling bits to other people was abstracted behind a bunch of buttons on iTunes Connect. This was such a powerful thing – I couldn't have had anything close to the moderate success I did without Apple's App Store strategy.
This is going to enable a new wave of great work for OS X. This platform already has some of the best shareware and freeware ever. Now that indie Mac devs will have an easy way to get paid, they'll be able to devote even more attention to their wares.