Pros
As a young person I find Morgan Stanley a great place to grow professionally and personally. The people at the firm are first class and you will form a life-long network of friends and industry professionals that you will WANT to maintain. The internal mobility program is very good and there often opportunity to travel. Management are likewise first rate and will not do work for the sake of doing work, but try to produce something meaningful or improve the firm, so work is always stimulating. Unlike other IB's which are currently culling to meet demands to cut heads, MS seems more committed to only doing this where absolutely necessary.
Cons
The current economic climate has meant that salaries have been growing very slowly and bonuses very very modest.