Vantaggi
When I signed on, the best reason to work there was name recognition and scope of projects. (Obviously, I managed to join at exactly the wrong time, as the collapse happened halfway through my contract.) The people I worked with generally seemed competent and professional, and I know that in our department our managers were really working to both protect and advance us -- circumstances just got in the way. The work I did at AIG set me up brilliantly for my next job.
Svantaggi
The current rending of the company limb from limb is a minus. I wouldn't dissuade people from joining now, because I think that things are beginning to get sorted out and the next few quarters will be better, but also be ready for some dead projects. When I left, I went through my folders and realized that every single one of my recent projects had stalled and died. If you think you can power through a dead zone for a while until the company finds its footing again, go for it. Another downside is the overuse of contractors: you never know who you're going to get on the other end of the phone, week to week, and there were some projects when all four of us at the table had only been at the company for a few weeks -- not good.