Pros
I have worked at PRH for more than 10 years, on both the Penguin side and the Random House side. Overall, I found Penguin to be more friendly and collaborative than Random House, but I've heard varying opinions from people all over the company. Every division and imprint has its own vibe.
Pros:
Great benefits
Fun/exciting/high-quality product
Some great coworkers
Upper management is proactive responding to an evolving marketplace, and has a vision for the future
Cons
Some not-so-great coworkers (lots of leeway given for "big personalities")
Low pay
Possible long hours depending on department
More junior employees may not always feel free to speak up depending on department