Pros
I work at Cycorp primarily as an ontologist, which means I get to represent facts and theories in a logical language (CycL) and put those theories to use in the form of query-driven, inference-engine-backed programs we develop for customers. Because Cyc is a general-purpose AI program, we are virtually unconstrained as to the kinds of projects and problems we take on. As a result, with each new project, I have the opportunity to learn about and gain a moderate level of expertise in a new subject-area, almost like being in graduate school, but without the tests and papers. Because the CycL language is so expressive, I never feel over-constrained or limited by the tools at my disposal when representing theories or crafting inference paths. The work can be difficult, and requires focus, intellectual curiosity, and the ability to think both logically and creatively. These requirements make for an environment that is both challenging and rewarding, intellectually.
Cons
Cycorp is a small company, and everyone on the technical staff is on relatively equal footing with respect to responsibilities, so there is little opportunity to "climb the ladder" here (which is why I only give Cycorp a 3-star rating for "Career Opportunities").
Cycorp executes its projects with extreme agility, so tasks and milestones can be dropped, extended, or added at what might seem like a moment's notice. This way of doing things isn't for everybody - certainly not for those with a pure nine-to-five mindset.