Although I agree that the jack-of-all-trades-master-of-none personality type doesn't make a good hire, the corollary to this is that you need to watch out for people with advanced not-my-job-syndrome. Over the years I've worked with designers who consider any mention of production of their work "techie speak", developers who think design is just "making things pretty", Flash guys who get the creepy-crawlies if they have to interface with Javascript, marketing drones who completely lack any understanding of how a web application is built, etc. Claiming to be a "specialist" is often just cover for a lack of intellectual curiosity.
People should of course always excel at a few specific things, and play off each others' strengths, but remember: specialization is for insects.