Pros
Fully fleshed out, from my perspective, IT organization. Everyone from the systems people, testers, developers and IT leadership run things like a well oiled machine. Any bad apples in the bunch are quickly managed typically with positive results (i.e. a reassignment rather than a termination). Development was held accountable to deliver but given the freedom to plan/manage their work. Strategy and data driven decisions. A lot of knowledge around the company and everyone is very eager to help. You will see horror stories of specific leaders in the organization on this site but I never experienced any of that. Flexible schedules, competitive pay, a lot of perks. A lot of opportunity to grow.
Cons
The non-compete agreement is very restrictive and they have been known to go after people who breach it. If you must sign a non-compete, make sure they are making it worth your while because there is nearly no career avenues past Overstock if that non-compete is enforced. Especially for IT.