Pros
Cisco is a well oiled machine. It has great support systems and if you like stability you will get on fine. If you are aggressive you will always have the opportunity to build a good niche and possibly a great team that will give you much satisfaction. But it won't be handed to you - you need to use your social networking skills to create the opportunity.
Cons
The sheer size makes if inefficient. If you come from the startup world that will wear on you after a while. One should stay at Cisco no more than 4 years in the same job. If you try and go external (to startups) you will be viewed as inflexible and some significant skepticism. This isn't always the case, but it is common to see people doing the same thing, getting stale and suddenly (maybe being pushed) to "see what is out there."