Guerrilla usability mary Deaton tells it like it is:

"Before we look at when and how to test, let's list some guiding principals:

• Test early and test often.

• Test the right people--only those who fit your user profile. If you do not have a user profile, create one.

• Avoid biasing the results in any way. The purpose of the test is not to win an argument but to find out how people actually use a Web site.

• Test only the things that are not strong conventions or standards. Don't waste your time or the company's money on problems that other people have solved."