Pros
Vanguard is a well respected company in an industry that deservedly gets very little. Clients are sincerely the focus of the organization and the products and services are top notch. Salespersons can genuinely have confidence in the solutions they are selling and others in the firm can "feel good" about the value they are providing for investors. For most positions, the job is easy. Performance expectations are low and very few people are working more than 40hrs a week. Even if they are, it's probably not necessary. There are plenty of "nice people" working at Vanguard. Co-workers are generally helpful and I've run across very few outright jerks across the company. Benefits are decent and Vanguard will pay for any number of graduate degrees and certifications.
Cons
Career advancement can be painfully slow and a very political process. Cash compensation is fair at best. There are low expectations for most positions and after a few years, this will suck the drive and ambition from many employees whose talent could be put to better use. While advanced education is encouraged, Vanguard will give its employees very little incentive to stick around once they have completed their MBA, CFP, CFA etc. They seem happy to allow their investment to migrate to competitors. I have never been in an organizations whose employees were so genuinely afraid of HR. Employees will rarely, if ever, be laid off or fired for incompetence. "Innapropriate" email or web usage, however, will have you escorted to the door in no time. "Innapropriate" is very vaguely defined. The organization as a whole is very bureaucratic and management doesn't seem to trust in the abilities of it crew. "Face time" is important even if it involves sitting around and reading the newspaper for a few hours if you have nothing else to do.