Vantaggi
Very strong IT engineering, lots of extremely smart people, plenty to learn, interesting tech challenges. Minimal formalism, engineers often have direct contacts with their business customers. Generally, there is very little balance, practically everybody I've met in different parts of organization were true professionals.
Svantaggi
Lack of formal testing organization. Production support is performed by developers (pager rotation), you'll often get paged in the middle of the night just to find out that something broke somewhere having nothing to do with what you are supporting and people have no clue whom to page. Engineers don't last long (many leave in 1-2 years), turnover is pretty high. Benefits are rather mediocre for a large company.