Pros
A lot of great people work here, and there are a lot of good connections to make. Everyone here is very helpful and friendly and there is a real communal feel at Genentech. The company really takes care of its employees as long as you are always honest with them. It doesn't really matter when you make a mistake, as long as you own it and admit that you did it management won't fire you.
Cons
One the biggest benefits is job security, however this can be a problem as well because you get a lot of people that are complacent and stop working hard. There is no real punishment or anything for being late or constantly being "sick" one day a week. Another big con of this place is that it is difficult to move around because so few jobs open up. Once you get into one of the departments its hard to move to higher positions just based on merit.