Windows Phone 7 might not launch with a catalog of apps of Apple's size, but Microsoft is going to one-up Apple in terms of app marketplace experience with refreshingly friendly implementation of trial-mode for apps for both end-users and developers.
In contrast to Apple app store, Microsoft's solution simplifies experience for users down to one app to download & run, and for developers, one app to submit to marketplace & one codebase to support. Microsoft implemented a licensing system into API that exposes to developers whether user is trialing the app or has purchased it. Developers can determine license with a single line of code "if (application.license = trial)" and adapt their app accordingly.
Microsoft is also giving developers free reign over what type of trial they want to do including butn't limited to reduced functionality or timed trials. At the same time, developers can easily create up-sell opportunities inside their app and because it's just a change of license, users can receive instant gratification without downloading new app.