Pros
Very high growth company. Fantastic benefits (they're even increasing 401k match in 2013... and there will be no increase in healthcare premiums) - stock purchase plan, equity for all, bonus program. It's wonderful working for a company that is growing and seems to be recession-proof. Global growth.
Cons
incredibly bureaucratic. SVPs are involved in nearly every decision. Very little autonomy, even for managers. Many micro-managers. The company is very cautious and doesn't seem to trust its employees - employees are blocked from viewing blogs at work. Facebook and twitter are blocked. There are about 400 people in the Woburn office, but at lunch everyone eats their desks (the cafeteria probably has about 10 small tables). Nobody seems to talk to each other. Most people don't see to be particularly happy, but stick around because of the great benefits. Don't get me wrong, American Tower is a very good place to work - but it's really not for everyone. I believe there are many changes under way to change the culture in a good way.