Toby Segaran, of Lazybase and tasktoy fame, recently emitted the following on motivation:
"The truth is that I don't make any money from these applications. They were never intended to be a business. I wrote them because I wanted them, it was an opportunity to learn something new, and like most people I love creating things. I determined that for less than I spend on coffee, I could put them online and share them with everyone."
In a recent conversation with a person from work I spoke about an idea for RSS aggregation I had that would be different from current tools but make for better use. As cool as it was, I said, I doubted I could build a business model around it. When it was suggested I came up with the thought as a way of making money, it gave me pause -

Not really, not at all, in fact. Things I write like iTunesBuilder, antiPod, Hobbitwerk:::pwd, Hobbitwerk::PIdigit, phoDak all had some personal problem or interest that prompted me to make them.

Pekka Himanen's book, The Hacker Ethic, does well on this note by giving "Hacker" culture three main attributes (from Wikipedia, I'd suggest you actually read the book):
1. enthusiasm, passion about work that is enjoyed

2. creativity, wish to realize oneself and one's ability, often in teams that are formed spontaneously (project orientation)

3. wish to share one's skills with a community having common goals, along with the need to acquire recognition from one's "tribe"; one is motivated by inner zeal rather than external awards: the fruits of one's work are donated to everybody for their advances and further developments
I would scarcely deign to mention myself in the same sentence as guys like Linus Torvalds or Toby Segaran, I understand this a lot from the stuff that I am trying to do. I'm hoping one of these days to have a good enough idea to make a contribution to programmers and people who use software.