Pros
I have really grown my career and skills at salesforce.com. I have been able to move from individual contributor, to manager, to a full executive. I have learned how to work with customers in a way I never could have at my previous employer, Oracle. I have also been able to grow my hiring skills, and even my firing skills. I have watched the management team take the company to an amazing market position. Best of all, salesforce.com keeps changing. When i started it was just about sales force automation. Then customer service, call centers, and portals. Then they invented Platform As a Service for customers and ISVs to build apps on the salesfoce.com force.com platform. Now we are entering Social Networking with Chatter which has redefined the company as a leader in an important new area. All of this has positively impacted me, and made my career skills more valuable than ever before. I get calls for different positions all the time, and they are increasingly exciting. But, when I compare them again where salesforce.com can take me, well, then I would be a fool to leave.
Cons
There is a huge amount of change all the time. The is the same side of the coin as growth. My priorities change at least once a year, and sometimes more. That has to be expected as we are fastest growing enterprise software company of our size. Of course, I could be at Oracle, and there would be no changes, because Oracle doesn't change---its only acquires. That is not what I want. Also, moving up at salesforce.com means I have to constantly prove myself. Its not about what I did yesterday, which may have been an amazing accomplishment, its about what I am doing today. We have grown so much I think we have pick up some dead wood, and management needs to be stronger about getting rid of the poor performers. We have a ton of stars, and a we have a few black holes. I am sure that happens when you grown from 0-5000 employees in 10 years. But, wow, we have really seen the changes happen. I can only imagine the next 10 years it is going to be spectacular with the new technology.