Pros
Wayfair is a fantastic place to grow. If you can prove that you're a superstar employee upper management will pay attention and opportunities for advancement will become available to you (after you've put in your time, generally about a year, not overnight like many people right out of college expect). They put a lot of trust in you and it's a great place to learn how to be a leader, master tools like excel and SQL and try your hand at everything from negotiation to project management. Work life balance is great and while the company expects a lot out of their employees they don't want anybody to kill themselves working- some are better at time management than others but not many people work much more than ~50-60 hours a week at all levels. As many others have mentioned culture is amazing. Many people make lifelong connections to other employees and create really robust networks. Most really care about their peers and enjoy spending time with each other in and outside of work.
Cons
Like many others have said pay is an issue and the reason most people leave. The company is beginning to right size things but it's still not anywhere close to market and has not adjusted salaries enough to the increasing cost of living in Boston. You also see a lot of bitterness and strife with certain employees who expect a lot of the company very quickly. The reality is that maybe 20% of entry level employees will get promoted, and you have to prove yourself worthy of these promotions. People who are not recognized get unhappy and the attitude can spread.