Pros
The benefits are good--everyone has a stock purchase option. They pay all medical premiums. It's a very secure job, no layoffs/mergers going on here. If you need a secure job and are ready to settle down, this is a good place to be. There are usually ways to further your career here, though raises or promotions... and they are very open to letting employees move parallel between groups to further their knowledge and experience. It was a great place to start a career or end a career, but I'm not sure it's where you want to be if you're mid-career and looking for a high paying or powerful job.
Cons
There isn't much accountability from management (there is no HR department). Compensation is a little low because of this, and your only avenue for raising issues goes straight through your immediate supervisor. Eek. Management has a TON of power here because of that. You don't have a way to air your complaints or voice concerns. If your supervisor doesn't like you, you are effectively screwed. They run the risk of conflicts-of-interest because there is no accountability among management... it's all about "who you know" in all jobs, but especially this one, because the team leads/supervisors have ALL the say in who they hire, who gets what raises, and what goes on. It's worked thus far, but with such a growing company it doesn't seem sustainable.