Jeff Atwood at Coding Horrors wrote a really good post comparing the details of his automatic cat feeders to the little details in your software. Below is my favorite line. Its a good read and lots to think about.
This is all your app is: a collection of tiny details.
This is still one of my favorite quotes about software. It's something we internalized heavily when building Stack Overflow. Getting the details right is the difference between something that delights, and something customers tolerate.
(Via Shawn Blanc)