Pros
You have complete choice in an extremely wide range of assignments, most of which is world class cutting edge work. Transferring between groups or even working in several is not discouraged. While actual policies are set at the group level, most groups are very tolerant of individual preferences for start times, schedule, time off, etc., making APL feel like a really easy going place. The corporate feel is in between a university and a large corporate company. Most of the work produced by APL is top notch so you can stand up and give that sales pitch without feeling that you are going to need an auxiliary closet for all of the skeletons. One of the biggest pros of APL is the lack of idiots. You know what I mean, every company has them. They start speaking in a meeting and you start to cringe and squirm in your seat. I have worked for and with a large number of companies, and APL has by far the lowest percentage of incompetence which is quite refreshing. And yet, this doesn't come with the "I'm better than you," attitude that can happen when to many brains are in one place.
Cons
Well not all is perfect in paradise. Management, just like management elsewhere, can still make themselves part of a good idea and screw it up. Luckily, this isn't overly prevalent, but it still happens. APL is a great place to advance oneself technically, unfortunately, career wise APL is a bit slower to advance. Leadership positions take longer to earn and come slower than in the corporate world. Pay is also slightly down from equivalent corporate positions, but on the other side of that, job security is very good. Unfortunately or fortunately depending on your point of view, the disparity in salary between the 10th and 90th percentile employee is not great enough in my opinion. Like many places, the best way to move up is to shift jobs/companies and then come back.