Pros
Like any big company, your job experience at Cisco will vary from group to group. The ideal situation in Cisco is to join a group which already has good mix of engineers at every level, and a strong upwardly mobile manager who trusts you and manages upwards well. If you can find this opportunity, and perform well, you will have the best career prospects. That said, the best thing about working for Cisco might just be that you if you are a competent and productive engineer, you have quite a bit of flexibility in defining your role and your contribution level. If you are really gunning for promotions, look for a good group, find a niche, take on roles that are difficult or un-wanted, and work your rear end off. If you want to coast and balance your time between work and other interests, then find a steady group, manage your time well, and you can stay safe in your job with just about 40 hours of work a week... and you might have the flexibility to telecommute or work from home. Another note - Cisco is a great place for competent women. There is a strong network of women employees and a tradition of mentorship, that really helps career growth.
Cons
The down-side of working at Cisco is that the salary is not great. And promotions & bonuses can get very competitive at the senior level. So, if end up in a group that is over-loaded with good people at your level and above, then you can get stuck in a situation where you are working hard but not getting enough rewards, bonus, or visibility. Actually, getting stuck in the wrong group can be a pretty bad experience over the long term. Talk to people and do your research before you accept any offer. Your manager is also very important. There are two types of managers you want to avoid. One (relatively rare) will use you to get ahead but not give you a fair share of recognition. The other (more common) one is a manager who is so swamped and has such little management insight / experience, that he or she is not able to help you with adequate guidance, especially when it comes to career development and growth. There is one other danger I must mention. This applies even in 'good' groups. There is a tendency at Cisco to just keep loading you with more and more responsibilities until you actually stand up and say enough. If this is an interesting job, you might find that you are spending more time on work than you had originally planned, at the expense of family, friends, etc. So decide for yourself how much you want to work and what your goals are. And then be prepared to work with your management to define the appropriate role. No one will come and ask you what you want at Cisco. You have to decide that for yourself, and then communicate it to your management. Also, if you do end up in a bad situation, be prepared to make an honest assessment of the situation and leave. No one likes to quit, but if you end up staying 5 or 6 years without fair rewards, you will find yourself falling well behind people who were your peers when you started... and this is really not a good experience.