Pros
MathWorks has several successful products and has been growing steadily for years. It has weathered the recession relatively well. Jack Little (the CEO) is a rational, principled leader who is in it for the long haul. For many people, the best part about working at the MathWorks is the stability and work-life balance. Stress levels are nonexistent and scheduling is flexible, although recently the work-from-home policy has been tightened significantly. As a developer you are pretty much free to do as you please. MATLAB and Simulink are cool products used by many people worldwide.
Cons
In some ways the MathWorks has been a victim of its own success. There hasn't been significant financial or market pressure on the company in recent times (if ever, except at the very beginning), and there is a surprising lack of accountability at all levels of the engineering organization. Individual contributors deliver shoddy work or slip features for multiple releases; managers run dysfunctional teams with massive turnover, poor strategy, and/or poor execution. All of this occurs with essentially zero consequence. Seriously. To some extent these problems are simply the result of low expectations and, again, the fact that the overall health of the company permits it. In some cases, appropriate networks of accountability do not appear to exist. Cronyism is also at work in certain networks within the organization. Mathworks is not a meritocracy. Advancement at the company is essentially entirely seniority-based. There is some lip-service paid to merit at review time, but the variation due to merit is minimal. Ultimately, it is primarily time served that leads to advancement. Coupled with the general lack of accountability in the organization, the result is that there is little ownership mentality and very little incentive to go the extra mile. Many employees have a very strong 9-5, just-clock-it-in mindset. The employees are not lazy; in fact they are responding rationally (it's a core value) to the complete lack of incentive to working hard and doing an exceptional job. Employees who complain about a lack of career growth are 100% justified. However, given that there is very little firing or other turnover of senior people, there is simply very little room in the org chart to promote anybody. The org chart therefore moves on geologic time and TMW is set up to slow the career growth of all employees (in terms of both salary and "rank") along given tracks. Remember that there are no rewards for being a "star." Ultimately whether you like TMW depends on what you want. I'd say that it is bad for the younger, ambitious type, and good for someone who wants a safe steady 9-5 with good perks, a comfortable work setting, and an exceptionally low stress level.