Pros
Fannie Mae has dug itself out of the hole it found itself in a few years ago. If you go in with your eyes open, it can be a stable environment with good work/life balance. The hours on the non-tech side are not very onerous and depending on your manager, working from home is a distinct possibility. Compensation seems to be above average, though not stellar.
Cons
This is not the place for someone looking to move quickly. Both in their day to day work, and their career mobility. It is very process heavy, though they're trying to reduce that a bit. In the division in which I work, there is not a lot of risk-taking or ownership. Particularly at mid-level mgmt, there seems to be a lot of risk aversion. It's understandable, given the company's history, but it's frustrating. I would guess that the federal government is going to milk Fannie and Freddie for all they, and not turn them back to their shareholders any time soon. Which means even more risk-aversion and a government worker attitude. Half the people I work with have PMPs. And most of those people are not really project managers.