MAG is currently in the final stages of production, with Zipper stress testing the online servers and ironing out some final bugs.  The game is due in just a bit more than 2 months on January 26, exclusively on the PS3.  It doesn't look like Zipper will be taking any time off, though - the Seattle-based developer is working on another, unannounced PS3 title. 

According to the LinkedIn profiles of several Zipper employees, the dev has been working on a second PS3 game for quite some time.  Graham Kay, a former Design Manager of Zipper Interactive, lists that he worked on 'Massive Action Game (PS3) & Unannounced project (PS3)'.  More recently, a senior software engineer for the company, wrote that he's currently "developing gameplay for two PS3 games".  Specifically, he works "on the core character team at Zipper developing gameplay to be used in both games currently under development for the PS3".

Earlier this summer, we spotted SOCOM 4 listed on PCB Production's credits page and theorized that Zipper could be working on the title.  It's increasingly looking more and more like this is the case.