Microsoft is accepting sign-ups for the beta, however a lot of people seem to be getting a "can't self nominate" error, which can be resolved by reporting it to customer support and they will send you a link.

Microsoft Flight approaches the virtual flight genre from the ground up, with the focus on the universal appeal of the experience of Flight. The simplicity of Microsoft Flight perfectly captures that vision while welcoming the millions of existing Flight Simulator fans. The new “Microsoft Flight” retains the full fidelity simulation longtime fans have come to expect while offering all players a whole new look and feel, a wide range of new game play and challenges, persistent experiences and social connectivity.

The Games for Windows Live platform sets the stage for all your virtual flight needs while connecting you to a global base of users, content and endless exploration. Microsoft Flight builds off its heritage of deep, immersive simulation and is redesigned to make the experience easier for virtual fliers of all interests and skills.

Games for Windows Live introduces a new level of connectivity to virtual flight, enhancing both the social and game play experiences of the title. Content is updated virtually. You can fly solo or join an entire global flight community online. You can easily connect with and facilitate flight experiences with your friends. The addition of Games for Windows - LIVE creates an ubiquitous virtual world of flight that offers easy and engaging access to the magic of flight for all.