The above blog entry tells the story of how one of the country's best restaurants maintains it's success. I'll give you a hint, it's not by lower prices.
The 5 observations that the author made could very easily apply to a web application. Consider #3:
3. Do something buzzworthy in the first few minutes. As the Cyrus hostess leads you from the bar/reception area, she stops just inside the dining room. There, she picks up a white Zsa-Zsa telephone and says into it: "Chef, the McConnell party is here for table 42. Please send someone out to greet them." It's startling and unexpected. Who calls the chef to say a guest has arrived? It was great theater. Restaurant reviewers can't help but talk about it.
A good web application should offer some feature which simply blows you away, and makes you wonder, how'd they do that?!.
Very good food for thought. (Sorry, couldn't resist the pun).