My homegrown saas application grosses ~$225k USD per year and growing. I started it in 2003 with $0 capital. I don't currently advertise, new business comes from seo and referrals. I am the sole developer/designer. (I use those titles loosely.)

What I have learned:

- Try to think about/plan for ten years out - Make your application easy/pleasant/fun to use for you and your customers - Limit third party dependencies at all junctures - Log everything, it makes support and monitoring easy and fast - Customers don't care what language/platform/db you use - Have a support ticket system - Have a coding convention/style and stick to it - Life work balance is important, take vacations - Run lots of backups - Keep it simple and thank yourself later!

Of course YMMV. Hope that's helpful to someone starting out.