I've recently seen the concept of delight in software brought up in a couple different places, and I just wanted to cheer it on.
Jesper at waffle is starting an open-source web browser project to revive the spirit of OmniWeb, called rouse. He coins the phrase "delight innovation". I love that phrase. He's talking about taking a browser, something that's relatively stable, and looking for ways to make it noticeably better again. I love that impulse - it's something I'm hoping to see in email clients too.
Another place that delight showed up (along with Surprise and Joy), was at 52 weeks of UX in a post called "design for delight". That post seemed to be a little more about the parts of design that don't affect functionality, but do add personality. I really agree with this angle too - I like a program that has little details that are just for fun.