In theory what is it?
In a nutshell: learning how to disseminate information fairly, legally, clearly and concisely, with adherence to Associated Press Style rules.
What is it used for?
For a wider variety than people think -- journalism majors go on to be newspaper reporters, copy editors, graphic designers, photographers, advertising execs, novelists, teachers, public relations execs, etc.
What does the major actually entail -- work-wise
Well, obviously you can expect to write A LOT. :) You must also have a good grasp of grammar before you start classes, because profs aren't going to have any patience for incomplete sentences, etc.
Required classes in my major included: Media History, Press Law & Ethics, Investigative Strategies, Photography, Editing, Layout & Design, as well as a myriad of different reporting classes.
What kind of jobs do you get with it?
See #2
Something really important about getting jobs, though:
You REALLY need to do as much hands-on as you can. Internships, fellowships, freelancing, student newspapers, etc.
You can tell someone how a newspaper works all day long, but you can't really understand it until you do it. Newspapers know this, and they really prefer at least one internship.
I had a full-time internship at a daily paper, two years in a senior position at my award-winning student paper, and lots of freelance gigs -- and I STILL got questioned about my experience or lack thereof.
What are the fellow students like (personalitywise) in it?
Hmm. Can't really think of any "types" that dominated the department.
Common Misconceptions
When I tell people I majored in journalism, they often assume this means that I want to be on the evening news. JOURNALISM is different from BROADCASTING, which usually falls under the category of Mass Communication or Radio/Television/Film.