One thing that's always bugged me about iOS is the dearth of options for sampling paid apps. Apple doesn't allow trials, and though some developers offer "lite" versions of their software for free, many don't. Finding the best app for a given task, then, can mean buying and uninstalling several apps before settling on a favorite.
Windows 8 will feature an iOS-like app store—the unimaginatively titled Windows Store—but happily, it won't force users into the same awkward position. As Microsoft details on the MSDN blog, the Windows Store will allow seven-day app trials, and it will have built-in functionality to make app trials hassle-free for both developers and users.
As a user, if you upgrade from the trial to the full version of an app, then all your settings and customizations will be preserved. Meanwhile, developers won't have to write their own safeguards to ensure trials users don't outlast their seven-day welcome. There will be "system functionality" to take care of that for them. APIs will be provided so trials can prompt users to upgrade to the full version, as well, and Microsoft will even offer "analytics to show the conversion process.
Making trials readily available will benefit users, of course, but it should also be a boon to developers. Microsoft comments that, on Windows Phone, it's seen paid apps with trials generate "up to 5 times" as much revenue as paid apps that lacked trials altogether. Being able to try before you buy is a powerful motivator, apparently—who would have thought?