Pros
Great office atmosphere - open office, snacks for sale, drinks on tap. The people are often intelligent and creative. The stuff you'll work on will give you insight into what's popular on the outside, but at the rate they're losing tenured employees (either through annual layoffs, the mass exodus that occurs right after the annual bonus payout in March, or through micro-management and middle managers that will sacrifice the team they're running for their own drive to a somewhat-higher class of middle management), there does not seem to be a bright future for this once world-class IT company.
Cons
They're cutting corners at every possible angle, and looking to sell off the company in sections. Outsourcing every possible role, but feeling the burn when it comes to losing tribal knowledge and skills.