Pros
The work is very interesting and R/GA has many high profile clients. The people are also extremely talented and one of the best things about R/GA is being able to work w/ these people (although I would exclude a good portion of the recent hires from this description). Also, the company compensates people very well as far as salary and health benefits go.
Cons
There is very little recognition for regular, everyday employees and the tiny bit that exists often times gets directed at the wrong people/person. Also, employees ping pong back and forth between here and other ad agencies. When people quit, you know that you are going to see them working again at R/GA again within a year or so, and that somehow they are going to end up being your boss. Another thing is that the work day can be a very long day indeed, much more than the standard 8 hours.