In theory what is it?
Physics. Theory and experiment.

What is it used for?
People with degrees or minors in physics work in any field which values critical thinking skills, mathematical dexterity, pattern analysis, or formal scientific skills. Accounting, fund management, banking, engineering, engineering management, medical physics, teaching, industrial research, quality control, sales, marketing, business, etc. etc. It also prepares one very well for advanced study in sciences, social sciences, humanities, law, medicine, or other professional programs.

What does the major actually entail -- work-wise
This is not a major for the faint of heart. The typical mathematics courses are Calculus I, Calculus II, Calculus III, Differential Equations, and possibly Linear Algebra. Classes in computer programming are usually necessary, and many programs require a minor--mine was Socio-Anthropology with an Archaeology emphasis. The actual Physics classes include the Intro series (I, II, and Modern), Mechanics I and II, Electricity and Magnetism I and II, Quantum, and sometimes Thermodynamics. That's the core; there are more Physics electives needed, and most programs require some sort of research project, paper research, or presentation.

If you intend to pursue physics through the Ph.D. program, you will take the hardest classes possible at any university. Classes in other disciplines (organic chem, molecular biology, for example) are very difficult, but they include a level of rote memorization that is more severe than physics courses, where you have to learn new and foreign ways to *think*.

What kind of jobs do you get with it?
I described a lot of this under "what is your major used for". There are so many "hidden physicists" working in all areas of industry and business that the American Institute of Physics is shifting focus to include Physicists outside of the "traditional" physics jobs, which are research, teaching, and College/University professorships.

Physicists are found in any industry/business where creativity, ability to think, and ability to analyze are highly valued. It is a great field to go into if you want to get into data analysis, investment analysis, management, or any of the traditional jobs.

What are the fellow students like (personalitywise) in it?
Generally fall into two categories:
1.) Very quiet, generally pale and undernourished. Often mistaken for computer science majors due to the lack of sunlight exposure. Examples: Hawking (pre-ALS), Sagan.

2.) Very outgoing and charming, oozing intelligence and friendliness, with a child-like curiosity hovering around them. Examples: Feynman, Einstein.

Common Misconceptions
That it's a "guy's" subject, that all Physicists are nerds, that Physicists aren't interested in anything but physics.