CircleDoc started as a hobby, born out of frustration with inability to work with others collaboratively when one team member has opened the "file". I was impressed with Google Docs and thought what if such a feature would be available in widely used application such as Microsoft PowerPoint. Using open source technologies such as Openfire Jabber server and IKVM (thank you), product quickly started taking shape. I launched it and LifeHacker picked it up which resulted into decent number of signups.
One lesson I learned from the entire process was that before launching a product, give a serious thought about how you are going to acquire your customers. Technical folks tend to ignore this and go with "build first and they will come" (read Vivek Wadhwa's Entrepreneur: You’re No Steve Jobs, So Look Before You Leap).
Having launched CircleDoc, this is what I am doing, listening to my early adopters and iterating.