Pros
O'Reilly's a "real" company, a market leader in the auto parts retail industry, selling both to auto repair shops and do-it-yourselfers with a chain of almost 4,000 stores nationwide. They have a mature management structure, a stable environment and, in these times, great benefits. They're a solid employer.
Cons
Being headquartered in Springfield, Missouri, a tiny town in the South-West corner of the state, their pool of corporate talent has been fairly limited and somewhat "inbred." (No "Deliverance" jokes, please!) They have an "intern" program at the local college, they hire their people directly out of there (or even out of high school) and promote almost exclusively from within. Result: An entire company with the attitude of "we've always done it this way." Don't expect to come in with fresh ideas and get anywhere.