BS in the Workplace

http://www.privacyrights.org/ar/employees-rights.htm

Can using your computer in a way that a business deems improper get you fired? And if so, what kind of legal action might you take against your place of business if your computer use gets you a pink slip?

Discussed here is the fact that businesses are allowed to spy on your computer use by using monitoring software. This seems like an infringement on personal privacy. People have lost their jobs over doing something as simple as checking their personal email from work and reading a joke that may be deemed offensive by someone other than the reader! Is this fair, right, and ethically a viable cause for termination?