A little testing is better than none

A really nice article in which Jakob Nielsen shows that even the tiniest amount of evidence (in this case, observing 2 users) vastly improves the probability of making correct design decisions.

...And, most important, we see how little users care about learning fancy Web techniques. People just want to get in, get their stuff done, and get out. They don't want to learn.

Guesses vs. data as basis for design recommendations - article by Jakob Nielsen