Pros
Catalyst is a company where employees time is valued. There are a large number of projects and clients and the company works hard to get people fit with the roles they want to pursue. Employees are encouraged to push new technologies. Everyone runs Linux, most people care about technology and talking to other staff is insightful and positive. There are also regular drink nights, free fruit and regular presentations about both company and personal projects.
Cons
The company uses a lot of open source technology to create closed source software. They do contribute back to some projects, but there are no specific rules about which licensing to support. Some technology is antiquated because of lack of software in the open source space for some of the things they try to accomplish.