Pros
Gartner has a deep knowledge-base on strategic IT-related issues, and employs hundreds of smart people to analyze very specific topics within IT (Research Analysts). When conducting a client engagement, you have access to much deeper information and expertise than you would at a Systems Integration consulting firm that performs IT strategy. This knowledge base helps you quickly gain expert knowledge and enables quality consulting delivery.
Kontras
Gartner is like a big University -- its employees (students) have to take responsibility to develop their own career paths. For those that want to learn and grow -- this is fantastic. This group represents about a third of the employee base -- probably the same as any big company.. For the other two-thirds who aren't go-getters, there isn't an an effective professional development curriculum to nurture them along. This would be fine if the low performers were managed out of the company, but unfortunately too many of them seem to hang around.