Pros
For junior staff, big accounts with money and a wide breadth of tactical executions. Opportunities to learn through training. Flexible on working from home. Decent salary and benefits that are in line with other large agencies. Two years ago Ogilvy & Mather (the advertising side) brought Ogilvy PR in line with its benefits, which meant the week off between Christmas and New Year's; four Fridays off during the summer (in addition to personal days, vacation and holidays); and unlimited sick time for SVPs and above.
Cons
In Washington, DC in particular, the office supports a culture of bullying and negativity. It's a very, very tough, harsh environment even though the office tries to pay lip service to "fun" with things like a happy hour bar cart on Fridays operated by the Social@ department members. Leaders (as defined as VP and above) who take credit for others' work and berate staff are rewarded, while those who stand up for others are viewed as "troublemakers." Ogilvy Washington regularly promotes staffers without giving them raises, but then charges clients the newly promoted rates. A lot of pressure on staffers at all levels to bring in new business.