If a client comes to you for a web site, the first thing you need to know is:
"Do you want the people visiting this site to notice it?"
It's a subtle but essential question.
For artists, musicians and web 2.0 companies, the answer is probably yes. Yes we want people to see the interface or remark on our skills or cleverness.
For everyone else, it's no. The purpose of the site is to tell a story or to generate some sort of action. And if the user notices the site, not the story, you've lost.
Amazingly, this means that not only can't the site be too cutting edge, clever or slick, it also can't be too horrible, garish or amateurish. It's sort of like the clothes you want the person giving a eulogy to wear. No Armani, no cutoff jeans.