Pros
Opportunity to work on great technology. In addition, the executive management is the best I've seen in working for various companies in Silicon Valley. Flexible work hours (though you need to work extremely hard). Varied set of products, so if you get bored doing something, you can move to something completely different without changing jobs.
Cons
Pay is not great: especially if you've been around for some time. Newcomers get paid market rates, while old-timers struggle to get raises. Raises are hard to come by, and are highly dependent on your manager and group. Middle management sucks. The executives are excellent, and their strategic vision has kept Cisco going, however, there's an enormous amount of deadwood, that needs cleaning. Too many directors sit around doing nothing and don;t get fired, in some ways its like getting tenure at Cisco to become a director. A lot of engineering will probably end up being moved to India, so watch out. Has gotten fairly bureaucratic, so getting things done is hard.