Pros
SI has some of the most dedicated, dynamic people I've ever had the pleasure of working with. The company is full of young, passionate staff who work hard, care about the quality of their inputs (often caring more than the client), and know their stuff. Management provides opportunities to grow and get involved in technical work far beyond what you get in similar companies. Recent changes in senior management have helped the dynamic (becoming action from above, not just below); and there are positive measures being taken to address work/life balance issues that have plagued the company for some time. The work is really interesting, and you have a good deal of autonomy to become involved in your areas of interest, build a portfolio you're interested in, and develop technical expertise.
Cons
Lots of initiatives and projects - and many (myself included) become overburdened and have a hard time saying no. This is partly because the work is interesting, and partly wanting to shield others from having to overwork.