I was just wondering if people could share their experiences and ideas about generating / earning income from a software product or service they have personally developed.

To me this seems like a good way to earn a living while doing what we love (programming) and working on projects and problems which interest us. Ie, NOT boring bank or marketing software etc 9-5 all week...

Some ideas I have are things like web 2.0 style sites (Facebook,Youtube,Twitter,Digg) etc etc... - These can be very very profitable as we all know but can take years to take off. Are there ways to survive until/if this does happen?

Mobile applications. Iphone, Google Android and the new up coming Nintendo DS app store. These have good potential to make it easy to find a market for your application and make selling it easy.

Shareware/PC software. A bit 80's and 90's and you kind of need to be a salesman/marketer to sell it but its the only other thing I can think of.

Also im not talking about doing freelance work. Im only interested in idea's you can come up with and develop your self (not other peoples ideas or problems which are you are payed to develop).

Things that a sole developer or at the most 2 developers could work on and have good potential for high returns on investment (in terms of time) would be great.

PS, I wish I thought of stackoverflow!