I still don't see what "having fun" has to do with "solving customer needs": often customer needs are boring, esoteric, poorly-specified, and technically uninteresting -- exactly the opposite of the sort of thing you'd do to "have fun".

Solving customer needs takes creativity. If you are having fun, you are more creative.

Dave Snowden has a theory that innovation is triggered by starvation of resources, time pressure for a result, and a shift in perspective. See http://www.cognitive-edge.com/blogs/dave/2006/10/culture_and... where he makes the point

   Creativity is just one way, and not necessarily the most    
   effective to achieve perspective shift.  In fact I am increasingly 
   of the opinion that creativity is not a cause of innovation, 
   but a property of innovation processes, its something that 
   you can use as evidence of innovation, but not to create it. 

He has some interesting short videos up on http://www.youtube.com/user/CognitiveEdge that address innovation issues.

This might be true, but coming up with solutions to customer needs is a very small part of making software. Most of the day is filled with programming, i.e. translating your vision into actual software.

Creativity is often the result of great adversity. But in a roundabout way, you're right (but probably not in the way you think). See, by having fun, you're wasting time you should be spending solving the problem. Then just before the deadline, you miraculously solve the problem. Your fun beget your laziness,which beget your desperation,which beget your creativity.

Fun might be the wrong word. My key point is that you'll be more productive and effective if you are loose and enjoying the process.

Except that if you're having fun, you will ignore things that are not fun at all, like figuring out how you're going to make money.

There's always some code that could be rewritten instead.

You will, otherwise you won't have any more fun because you ran out of money.

Nope, that doesn't stop lots of people. Ever heard of Duke Nukem Forever? Or any of the people here on HN who talk about their social network for dogs-type startups.