Well, it's very hard to generalize about any group of people, much less a group as diverse and unique as the folks who work in libraries. But I'm going to make a few sweeping statements, any way -- what the heck!
In more than 20 years of working in academic libraries (and one short stint in a state government library), I have observed that libraries draw an unusually intelligent group of people. Many are very learned, some are hugely over-qualified for the jobs they are in. I include in this observation both the professional librarians and the paraprofessionals and clerical level.
You get people who like to learn, and value knowledge. Maybe because libraries are places to keep learning, just through your work. Also, because some of the schools have the wonderful perk of tuition remission, libraries draw people who like to keep learning. In recent years, you could not stay in libraries without learning, learning and learning -- about changes in publishers, about technology and library automation systems, about Boolean searching and Natural Language searching and about teaching techniques both old-fashioned and new-technical, and about managing people.
There are so many different kinds of people in the "library machines" I have known. Conservatives, liberals, radicals, anarchists and utopians on the political spectrum. Many -- but not all! -- display those characteristics that show up in so many library job postings: meticulous attention to detail. Some are real detail fiends, and make the library a place of order and reason. Others are visionaries who look at big pictures and dream the future. But every single one I can call to mind, certainly fits the two characteristics above: Smart people who love and value learning. They have boundless curiousity and a passion for education. Oh, yes, one more unifying characteristic:
Library people are committed to civility and community. I have seen such a change in the people I work with between the time I worked as a lawyer and the years I have been a librarian. Librarians are seriously into community, collegiality and sharing (except the last donut, of course, but that would be asking too much!)