I'm not going to cover everything in-depth, since if you're a Windows developer, you're probably already pouring over the documentation and developer agreements as we speak. The gist is that Microsoft asks for the same 30-70 split Apple employs, but they're being nice by stating that if you earn more than $25000, Microsoft will only cut its, eh, cut from 30% to 20%.
You can price your application between $1.49 and $999, which seems a bit odd. There's not going to be any $0.99 applications this way, and truly professional applications, like Photoshop, touch close to the maximum price. Of course, your application can also be free, and like the store on Windows Phone 7, Microsoft supports trials and in-application purchasing, and implements sales analytics as well.
Another interesting difference between the Windows Store and the Mac App Store has to do with subscriptions. "Developers can also choose to manage their customer transactions directly, for example, with newspaper subscriptions, or to adopt a business model with offline fulfillment, such as for auctions," the company details, "We don't mandate a specific transaction engine and developers can use their own. They can also choose the ad control that works best for them."
I'm very happy Microsoft has taken open source into account, probably because I'm sure many Microsoft employees want to use Firefox as well. As the App Developer Agreement details:
In other words, an open source license may contradict Microsoft's own terms so that open source software can be distributed in the Windows Store. This is very good news. Sadly, there's no word yet on sideloading, or the ability to distribute Metro applications outside of the Windows Store.