It's not just for e-books, you can make it work for any product or service you sell. Some subscriptions that might work for your product could be:

- e-mail/telephone consulting

- a private or members only web site

- print newsletters/magazines

- product updates

- subscription warrantees

- product insurance

- e-zine/webzines

- the ideas are endless.....

The subscription product should be related to the product or service you're selling. You could charge a weekly, monthly, or yearly subscription for the upsell product. You could sell your main product and upsell product as a total subscription package deal. You wouldn't charge the one-time price for your main product; you would just charge the basic subscription price of the upsell product.

The major benefits are that you don't have to keep creating new upsell and back end products. Once you get enough subscribers you won't have to sell anymore, you just keep generating income from your current subscribers. You would only have to sell again if you lost a lot of subscribers.