Pros
For me, it's the work-life balance. I'm not expected to give my life to the company, and (at least in my area) there's a get your stuff done, do it well, and then go home and have a life mentality. Obviously, your mileage will vary depending on management in your area. But then there are plenty of places to move to, and they've recently made it easier to move around within the company. Compensation is fair (cost of living is low, which helps). The atmosphere is not what you'd expect--it's very laid back, casual, and friendly. Now if only they'd brighten the place up a bit and add some color... It's a great place to be if you're a family person and want opportunities to grow without burning yourself out.
Cons
Typical big corporation stuff: we're big and there's always red tape and paperwork involved to get anytthing done. Then there's the fact that we're a stodgy, conservative insurance company which means we're way behind the technical curve because we test the heck out of everything before implementing it. Good for stability, bad for boredom. Tools, infrastructure, and process all get in the way of development speed and make work sometimes frustrating--but these are good areas for smart people to come in and make a difference.