Pros
GS attracts some of the most smartest people who are also some of the most ambitious and competitive. A fast learner will experience a fascinating amount of growth after the first few months of joining, simply because working with tough, strong people makes you stronger. It is also a brand name company that looks good on a resume.
Cons
There is little room for personal life. First line support is a full-time job by itself but developers are expected to do that AND development. Tokyo is not a good place for anyone who wants to develop good software engineering skills, since all good projects are built out of New York or London, and then get refitted to tokyo, Tokyo technolgists are usually left with a blackbox and they have to figure out how to make it work with the rest of the systems, which gets very mundane. An IT employee will find himself becoming less marketable for positions outside the firm the longer he stays in the company. Most of the technologies in GS are based on a firm-wide proprietary system, and so technologists develop skills that are useless outside of GS. There is a reluctance to adopt new technologies that are common in the market place.