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.
