Those of you who have been around for some time are probably familiar with Steve Pavlina. This article of his is something I go back and read regularly, and I’ve probably read it 10+ times by now because it’s so clarifying, inspiring and instructive. The article is pretty old but you can just replace “shareware” with “SaaS” and all the principles still apply.
http://www.sodaware.net/dev/articles/shareware-amateurs-vs-shareware-professionals.htm