But not all subscription-only functionality. Microsoft is touting it as a chance to "enjoy all of the customized entertainment app experiences featured on the Xbox LIVE service." It's all about the TV services, and unlike most XBL free weekends, "Multi-player gaming will not be unlocked in this promotion."
In addition to free access to apps like Crackle, Syfy, and Vudu, you can get a free trial of Hulu Plus, Netflix, or EPIX during this period (really, you can get a free trial of Hulu Plus or Netflix any time!). The full list of apps is posted on the promotion's site.