The first event next month is being held in New York on January 18, 2012 (from 11:00 AM to 9:00 PM EST). The second is being held in Boston on January 20, 2012 (from 11:00 AM to 11:00 PM EST). Both will be all about building social mobile apps; Facebook will cover iOS, Android, and mobile web (HTML5) app development.
Although the first Mobile Hack was free for everyone, these two events are not. Still, General Admission is pretty cheap: just $25. Furthermore, there is an option for students to attend the Boston event for free.
At the event, industry experts that have already built social mobile apps will share their best practices. Along with the Facebook Platform team, they will show you how to make your apps more social and how to leverage social discovery.
At the end of the event, the best apps will be selected by a panel of experts and prizes will be awarded. Your app does not need to be created from scratch at the event, so you should start coding now, if you haven't already.
Events like this one are a great opportunity not just to learn from Facebook but from your peers in the industry. You should take advantage while Facebook keeps the price tag low: chances are in a few years these mobile events will be as expensive as the desktop ones.