Pros
You can expect an honest working environment at Overstock.com. The first thing that they tell you when you're hired is "If you're caught in a lie, there goes your job." I've had a few difference managers, all of which have good support for family values, work ethic, and schedule flexibility. The pay is great, and the hiring process is rigorous enough that few (if any) slackers get hired.
Cons
Although there are opportunities for advancement within the company, most of them are management positions. There are few opportunities to advance purely on a technology level, even though the IT department (software dev, operations, etc) is quite large. Unless you are in management, don't expect anyone in management to really listen to your ideas. Even if you've been with the company for years, the lack of advance in job title says a lot.