A type of computer user that takes advantage of as many system features as possible to achieve maximum productivity.
There is a certain line between power users and hackers. Often, power users are just end users; They don't program stuff, or at least nothing complicated. But they aren't afraid to use keyboard shortcuts, obscure utilities, less often needed features, and write (short) scripts or macros if it's needed. A power user would use a reasonably stable beta versions, while hackers would use not-that-stable betas, because at least they know why it doesn't work =)
Contrast: afraid of computers, "I don't know, I'm just working here".