This great review of Steve Krug's book is well worth clicking over to, even if you don't want the book: Accessify.com - Book Review: Don't Make Me Think, Steve Krug. A common sense approach to web usability.
Here's the extract that caught my eye:
We're thinking 'great literature' (or at least 'product brochure'), while the user's reality is much closer to 'billboard going by at 60 miles per hour'
Yes indeed. We do tend to think our corner of the world is central to the lives of our customers, not just our own. A good reason to do experiential research, so we put ourselves in the shoes of our customers, in the same context they have as much as possible.