After Apple released Game Center, OpenFeint's survival plan was to provide even more services on top of the Game Center functionality, now OpenFeint X hopes to cash in on this. It's a service that allows iOS developers (plus other mobile platforms) to add over-the-air purchasable content to their games on top of Apple's already popular in-app purchasing. OpenFeint X works outside of Apple's store, and allows devs to quickly add in-app content without going through Apple's approval system. Only a few devs have worked with it so far, but it's new and more will surely follow soon, especially after their "Million Dollar Challenge" announcement.
OpenFeint's "Million Dollar Challenge" has been issued - the first 100 devs to sign up and use OpenFeint X can earn up to $10,000 without sharing any of their revenue. After that, devs who use OpenFeint X will have to share their revenue (more details on the link).
This really won't affect end users, a tap is a tap, but OpenFeint X will be an interesting alternative or option for devs to make. As revenues continue to grow from in-app purchases, OpenFeint X couldn't have better timing.
For some reason since Game Center arrived, if I see an app icon with an OpenFeint badge (or Crystal, Plus+, etc.), I'm usually not interested anymore. I don't know why, there's nothing wrong with any of these alternative services but my heart and wallet goes to Apple and its products and services.