Startup Valuation – How do Experienced Angels Value a Startup?

When it comes to valuing a startup, some people say it is more art than science or that you are really taking a shot in the dark.  Many angels will start with where the company is today and try to determine a valuation based on the current condition of the startup.  They may start with a low valuation and add to it depending on where the company is in its process – i.e. Do they have early revenue? Do they have stable customers? Are they profitable? etc.