Pros
All the benefits you could imagine are available to you. You'll work with really smart, competitive people. You will probably do the best work of your career at Salesforce.com. You will build a network of amazing colleagues, and you will experience projects, processes, and work that is absolutely the cutting edge. If possible to work in San Francisco, that's the best place where all the really great things about Salesforce.com come together.
Cons
After 3 years you will be burned out and no further ahead in your career. If you find you are not burned out, congratulations! You are among the super-humans who can handle working 60 hours a week, playing politics, and working in a whirlwind environment. You know who you are - you run triathalons and scale mountains! If, however, you wish to have a balance in life, after 3 years you will start to look elsewhere for your next career move. Having Salesforce.com on your resume will open many doors for you, so you can take your career in any direction - start-up, mid-sized company, start out on your own, large company - you name it! So go ahead, take that job at Salesforce.com, just know it's a step in the right direction toward where you really want to be!