If you are close to retirement this is a good place to be; If you are young stay for 3-5 years and then leave.
Pros
It is a good stable place to work at; people are nice in general - very collegial atmosphere; people are very smart in general - lots of Masters/PhDs who know their stuff and know how to apply them to practical problems. People try to do good stuff and more often then not are working on something interesting. Company has seen continuous growth throughout its existence so far - Jack and others have made wise choices that have enabled them to weather some fairly serious economic storms. Layoffs are not common but are done in a hush-hush way. You get to interact with customers directly esp if you are in technical roles who most of the times respect the company and are very willing to share information - I have seen more doors open for MathWorks than any other place.
Cons
Smacks of bureaucracy with processes, middle managers etc.. Lack of career growth opportunities or even clear directions/paths is just mind boggling. There is absolutely no clarity in how to go from one level to another. Promotions are non-existent. Constantly understaffed because of which projects go under resourced, or don't get completed. Contributing factor I think is that some of the good people leave because of median to less than median pay, lack of growth opps. Information sharing between groups is not efficient even for a fairly small company. But in its defense it is probably a function of rapid growth it has seen over past few years. Not nimble enough - MathWorks doesn't have serious competition and that is why it has survived for so long. Lack of competition could just be a function of the diverse portfolio of products and industries in which it operates. MathWorks is increasingly looking Microsoft of technical computing world minus the evilness part.