Pros
McMaster Carr is excessively fair. No one plays around on Facebook or does anything else beside work during scheduled hours, and some people consider that culture restrictive. However, in return for putting in 8 solid hours of work per day, you get 1) unheard-of retirement benefits and excellent healthcare 2) the guarantee that your job will never make you work long hours (if you do, you're very well compensated for it--not like other companies that expect salaried employees to just suck it up) 3) a fast promotion track for management. I won't lie, people tend to love it or hate it, but if you're smart, quick to catch on, someone who thrives in a sink-or-swim environment, and someone who is excited by business problems you can sink your teeth into, McMaster Carr is one of the best companies out there to work for. It is an exceptionally ethical and well balanced work environment. I almost didn't take my job offer with them due to the negative reviews here, but my experience could not be more at odds with the experiences posted here. Take the chance--this company fast tracks you to financial security and business impact.
Cons
It is a sink-or-swim environment. Job security is earned, not guaranteed--we don't sign contracts. And that's really scary for some people (rightfully so.) Non-management employees are held to strict measurable standards and a certain number of errors equals no more job. For management, if they don't feel that you have potential to move up or if you are not having a measurable impact, you could be let go. However, this should never be a surprise. Do good work, be proactive, and you will be successful.