Vantaggi
There are great benefits. Plenty of commuter/parking perks. There's an onsite health clinic, though I've never personally used, colleagues who have used it give it high marks. There are also a few programs for discounts on travel, products, services.
Svantaggi
I think working here is like any other corporate environment... sure, there are opportunities to advance, and putting in hard work along with a little self promotion will help move you along. However, there are some folks in management, mid-management who seem to value the big talkers over people who can actually do great work. It doesn't happen all the time, but I've seen enough talented people get pushed aside because they are either not a part of the "in" crowd, or simply grow frustrated of the fraternity of "oh, I know you from" and "you worked at one of the big three nets, you must be smart" type folks. It can be discouraging... but at the same time, managers seem to be cycled in and out every 3/4 years, so if you stick around long enough, maybe you'll get lucky and move ahead.