Pros
Gallup is a Dr. Jekyll/Mr. Hyde kind of company. Their pedigree is top-drawer along with much of the science they use. Gallup has done some of the world's best beta research, especially research about how best to conduct research. The Gallup name is probably the strongest part of the company, dating back to people like Dr. Gallup and Don Clifton. Having worked at Gallup gives one immediate credibility when looking for another job, which MANY people have found it necessary to do in recent years.
Cons
Gallup authors have written several business best-selling books, but the reason for much of the big book sale dynamic is that they give a copy of every book to every employee and their books serve largely as infomercials sold enmasse to clients. Gallup's current senior management tends toward the belief that THEY are the visionaries who put Gallup on the map. Kind of like the fact that the width of cracks in the sidewalk are highly correlated with the murder rate in NYC - correlation doesn't always equal causality. The current senior management was with the company when Gallup made its greatest revenue strides, but the company's main visionaries were Dr. George Gallup and Dr. Don Clifton, both of whom are deceased. Retaining control of the company is senior management's highest priority, and they have caused massive bloodletting in recent years to achieve that objective. Probably the best evidence of that observation is the fact that the company's growth stalled as the number of new clients fell below the number of ex-clients. For a company that hangs its hat on the mantra that organizations need to treat their employees well in order to achieve top performance, many of Gallup's ex-employees and dispirited current employees would attest that the company has had enormous difficulty practicing what it preaches.