> If you asked someone to draw the screen of say http://godaddy.com from memory, they'd likely mainly remember the lovely lady wearing a 'godaddy' t-shirt. Is that the most important thing?

That's exactly the point. Isn't that something the GoDaddy designer(s) should know and take into account? They want people buying domain names, not drooling.

Again with GoDaddy, do you want a sexy brand image, a lead gen wet dream, people to quickly buy domain names in bulk, etc.? I completely agree that "important" isn't specific enough but it's up to you, as the designer, to figure out the balance.