Pros
First of all PayPal is a very successful business so you are pretty much guarantied a stable employment. Benefits are pretty good: nice matching 401k, employee stock purchase plan, stock grant (!) instead of stupid stock options, pre-tax flex spending account, bonus program, school reimbursement, vacation/holidays etc. But medical could be better - for a family coverage you'll have a pretty sizeable paycheck deduction. Campus on North 1st is great, has a free Club One gym, ping-pong, billiard, basketball, tennis and a great soccer field. Work-related: planned, process-driven, structured environment where things progress slowly but surely. As soon as you are involved in projects you start going to many meetings (for some people too many). You will communicate and coordinate across many different teams. You will learn a lot (or at least something) abou online payments and electronic payment types. More reason to work for PayPal: great company name on your resume, being a part of something so big is likely to make you feel good, meeting new, talented people. Overall PayPal is a great place to get away from the startup rush, settle down, start a family, have kids, remodel your house, etc. Things do intensify a little around the pre-release bug-fixing stage.
Cons
If you are an engineer (coder) you'll probably use about 20% of you skill set and your learning will be limited mostly to things that are very specific to PayPal. If you want to continue to innovate and learn new technologies you'll have to do it mostly on your free time. You can also take some classes offered by PayPal that are useless for the most part but you'll need them so that you can write about it in your self evaluation. As far as career advancement goes, you'll have to talk a lot with or without reason or purpose and stick your nose everywhere. In every meeting propose things that nobody will ever do, ask meaningless questions, give meaningless answers, build castles in the air - and you are golden! To be fair I must say that if you actually bust your ass doing YOUR job you may also get noticed but it's a much harder way and will take longer.