Pros
You can certainly gain a lot of office environment experience here. The hiring process is lengthy, but once you're in, you're in. The hours are stable if you're not one of the On-Call "star" employees.
Cons
The pay is low, and remains low after years of working here. Your responsibilities can completely change, dramatically increase, and will all be micromanaged and scrutinized by upper management as though you're making site manager level salaries. Odds are, IST pays lower than other companies in your area for the same, if not less work. Site managers can be proven problems who cause multiple employees to quit, and will not even be given reprimands. PTO is given out extremely sparingly, taken away by their screwy holiday system, and the CEO seems to find it entertaining to make employees compete against each other in "fun" little games like online mock-auctions for precious PTO days. You can and will be thrown under the bus if you are not careful. Depending on your site, people in higher positions may regularly threaten your job over minor issues. The benefits are a sick joke: their medical insurance costs more than you'll make in a month starting out. There are retail jobs that provide more benefits than IST. You're told at the start that they're big on promotion from within. Do not get suckered in by this. The arduous process of being put on the path to being ELIGIBLE for promotion is really just another way to squeeze value and effort out of you while continuing to pay you very little.