Pros
Great culture, vision, passion, compensation, and benefits. Interesting work which you can, to a great extent guide. Lots of room for creativity and opportunity to work with very large scale, high quality and cutting edge infrastructure. You will also have the opportunity to work with some of the friendliest and smartest people you will ever meet.
Cons
Everyone is SO SMART rockstar engineers come to Twitter and can feel a little less special than they are used to. It takes some time to get up to speed on many custom systems. Documentation is lacking and there is too much dependance on tribal knowledge. Valuation is currently lower that it should be, leading to sadness for some, but the roadmap is strong and the company is on the right track.