Im currently doing this, but not the "traditional" way.
I am using wordpress as a basis and have developed a distribution
system in which users can sign up, pay on a monthly basis, and get their own business website ready within 5 minutes. They can choose between 5 premium themes and are able to configure everything themselves. We do offer instructions on how to do the most common things.
If they want premium plugings/themes they will have to buy this as an addon.
Basically its a premium wordpress hosting business targeting to small/medium sized business owners who dont want to spend thousands for a premium website. They more or less get the website for free and pay for hosting/support and functionality.
If they want they can buy different services (like unique webdesign/ let us do the website for them), SEO, Logo and print,etc. for a fixed price.
The whole distribution process (signup,billing,invoicing,wordpress website creation, domain registration) is completely automated.
They even get reminders/auto shutdown when they haven´t paid in certain time period.
They monthly fee varies depending on disk space, plugins/themes available, traffic, emails, and support level.
They can cancel and up/downgrade anytime.
I´m currently into late developing stage but have got some very satisfied paying customers and have many prospects who are very interested in this.
If you have any questions regarding this, I will try to answer your question as precise as possible.
Regards from Germany