Maybe the reason why persuasive web site design fascinates me so much is because I'm a cold call sales person's worst nightmare. The best invention ever made was "Caller ID". They want me at the wrong time.
For a web site or web-based application to rock someone's world, many factors have to miraculously kick into place at once. They may be credibility, trust, easy to read content, etc. And you can still miss your mark because you didn't take into account your target users' mental or emotional state.
Say you have a weight loss product web site. Customers can order more products online.
Why do they come?
1. Because their doctor told them to lose weight and eat healthier? What state of mind is the potential customer in then?
2. Because someone called them "Fat"? Perhaps they've arrived to the site and want to be comforted.
3. To purchase for someone else? They may know what they need and will expect fast, direct access with no browsing.
4. They've just ate a brownie! They want to starve for a week. Does the site have a section for rescue, with call to action prompts to suggestions for what to eat so they don't punish themselves?
This is why search behavior is so meaningful and dangerously overlooked by companies.
Cre8asiteforums members amuse themselves with this topic in Do You Know All The Who's, For Whom You Are Developing?