Pros
As an engineer I think some of the best reasons to work for Cisco is the opportunity to work on a wide variety of technologies. In my business unit (GSBU), people do have the freedom to work on technologies that they find interesting. Also, the stability of working for the industry leader is nice. In some ways, the benefits are better than any other company I have worked at (4 weeks of vacation).
Cons
Recognition and promotions are difficult to come by. It seems as if promotions have more to do with "ass kissing" than merit or accomplishments. Also, it's not likely that you're going to make rapid career advancements. This is a big company with a pecking order in place. If climbing the career ladder quicker is your priority, Cisco (or any large company for that matter) is not your place.