Pros
Riverbed is a growing company that is willing to venture into uncharted territory but at the same time wants to maintain its lead in the market with other products. This gives engineers a lot of opportunity to do what they like doing without the red tape that big companies require or the level of risk that small companies are exposed to. Many development groups are given a good deal of independence, but there are always a few on each team that work to integrate the product lines, too. Acceptable IT department. Responsive to employee requests. No skimping on the free drinks and snacks.
Cons
Private companies don't have a good mechanism to issue options or stocks, so the only ones with a share in the profits have been there a couple years. If that share of the company turns out to be a windfall, there could be a divide between the haves and have-nots. IT is actually better at Riverbed than nearly every company I've worked at (6), but it still is tedious. Often the laptops issued to employees are last years models and the support for OS X is pitiful (i.e., still using Office 2012).