Pros
I've seen some bad reviews on Glassdoor about working at IS&T at Apple, and I feel compelled to share my experience there because I think it was actually pretty great. Some aspects of corporate culture that I see shared by most (if not all) areas in apple: 1) A standard of excellence, which can be extremely satisfying for perfectionists. At other companies that I have worked, there tends to be a mentality that as soon as something is 'good enough' it is pushed into QA or production. At Apple, things don't move forward until they are excellent. 2) Passion for work. I've never been at a large company where employees are genuinely this passionate about their work. You won't encounter any of the apathy that you often find in large corporations. 3) Cool problems. Numbers 1) and 2) are arguably made possible on a widespread level within the company because the problems that engineers are working to solve can be extremely interesting. Additionally, solutions almost always have a large footprint of impact due to the number of people who interact with Apple products on a day-to-day basis. You won't find yourself doing anything remedial. So now the question becomes- how are things different in IS&T from other parts of the company? The answer is that it doesn't really. If anything, the impact of what you are working on is larger than in some other areas because a lot of what IS&T does is the foundation that makes consumer facing products possible to run on. There are entire companies out there that *only* make a one of the products that a given team in IS&T produces, and there is a good chance that IS&T is doing a better job of it. While all the teams in IS&T are different, I think that these general principles are true for all of them.
Cons
One of the things that I found challenging was the modularity of the teams. By that, I mean that the teams in IS&T don't interact much with other teams except for when they have to for business reasons. Socially speaking, I don't see a lot of full time employees eating lunch with people from other teams that often. Also, within my own team I never really felt like I had a strong social connection to the people I worked with- people were often just coming in and doing their own work without really interacting that much with other people in the cubes around them. This means that in order to make work friends you kind of have to go out of your way to initiate contact with other people, which can make the first couple months of work a little tougher. This was my experience and I have also heard it echoed by other people in IS&T.