Apple: Master of Miracles
Right now, there's a significant number of open source and/or free applications for the Mac that I use regularly, from small utilities like MenuMeters, Flux, and Caffeine, to apps like CoRD, Chax, Plex, SuperDuper, Songbird, GlimmerBlocker, and many more. You can find them at various places around the Web, and downloading and installing them is extremely simple, as are most application installations on the Mac. The Mac App store won't add much to what is an already simple process, but it will collect them into a central, searchable marketplace.
The one thing most of these utilities have in common is a PayPal donation button on the download page. The apps are free, but the developers are hoping that some folks will click that button and send them a few bucks for their efforts. While they make some money this way, it's not very much. Once Lion is released, I fully expect these utilities to move to the new Mac app store and be available for a few bucks. The end result is much more exposure for these utilities and, most likely, a more stable revenue stream for the developers.
There's also likely to be another app store gold rush, as we saw with the iPhone, but it'll probably be lower-key. Tales of 99-cent flashlight apps generating hundreds or thousands of dollars a week for a few lucky souls abounded when Apple launched the iPhone app store, and there will be analogues in the new app store, but they'll probably be fewer in number.
The reason for this is that people are far more likely to buy an app for their iPhone on impulse when a friend shows them the app on their phone, but when you're at home on your computer, you're less likely to have that direct introduction. There's also the fact that there are more iOS devices out in the world than Macs.
But that might be step nine of Jobs' plan: Make the Mac so irresistible to the millions on non-Mac people who have been conditioned to the Apple computing ecosystem through their iPhones and iPads, that buying that iMac becomes the next logical step. That sounds far easier said than done, but then again, so do each of the odd-numbered steps outlined above.
At this point, I wouldn't put anything past Apple. It appears to have cornered the market on miracles.