IMO the Mac App store is going to be a very big deal with ramifications far beyond the Mac user base. It is going to drive changes in app delivery (obviously), license and upgrade pricing, and the definition of a “meets min” application. Not just for Macs but for Windows too. Expect to see more “bite size” apps a la smartphone apps. Also expect to see in-app purchasing down the road.
These effects won’t be limited to just the Consumer space. I expect the ripples to be felt in the Enterprise space within the year.