Pros
Lot's of free food and T-Shirts (but interestingly no coffee!). Working at Atlasssian was a great resume builder, but probably the worst job I've had.
Cons
Atlasssian is a very very very cliquey place. If you don't fall in with the right crowd or have different opinions, you're not going to do well there. When I worked there I was amazed at the amount of internal politics, and how everything is decided by committee. There are also a lot of people who've been there forever but don't really have any job definition. They're just kinda buddies with the founders and so they stick around. Lot's of trolling on things like internal Blog posts. In short it was just a very poor experience. I felt like I was in some kind of cult where everyone was drinking the Koolaid in public but behind closed doors everyone whined about how the company was being run. For their part, the founders have made their money, and have started investing in other startups and even getting involved in the Australian political scene to a certain extent, so they're pretty checked out. The pay was lower than average, but like Google in the early days lots of people were willing to take that in return for having Atlasssian on their resume (I know I was!).