Pros
Red Hat is a meritocracy. If you put in the hours, do good work, always work to improve your skillset and advocate for yourself, you will find success. I hired in as a Consultant with no tech degree (self taught Java). Through hard work and advocating for myself, I made it to Consulting Architect in 6 years. Others have done it much faster. Even though the company has become more corporate as it has grown, there is still a Wild West sense to some of the divisions (I've worked in 3 different divisions over 10 years). With that chaos lies opportunity, but also unease if you desire more structure. Be cognizant of this when hiring into a division. If the division culture is too staid or not startup-y enough, transfers are usually allowed. I very much enjoy working with other people at Red Hat. Even though we come from a relatively diverse set of backgrounds (by tech's standards), we all have common ground in the work we do and the culture of the company. If you are passionate about something tangentially related to your work, you are encouraged to pursue that. Whether that be building a rack, writing bootstrapping code or working on open source projects, Red Hat rewards go-getters.
Cons
The acquisition by IBM hangs over the company. There is a sense that if RH slips in growth or profits once, the IBM overlords will assimilate our culture to be more like IBM to 'fix' us. While this may not be true, that potentiality is openly discussed. Some of the software suites RH develops have lofty physical requirements. Many employees that have to deal wth that software in a daily capacity have had to resort to building their own home labs in order to run the software to learn and resolve client issues.