No development details or release dates were mentioned. Given the casual nature of this announcement, however, one can assume that both Gears and UT3 will be ported from the PC to OS X using Cider, rather than being developed natively. No love for PowerPC users; though it might be time to consider that Intel-based Apple you've been eyeing ...
[Update: It appears these are coming to the Mac natively, not through the magic of Cider, according to this comment from MacSoft's Ryan Gordon: "And no, neither game is using Cider." Impressive. Thanks for the link, David!]
Microsoft Xbox 360