Is it worth it to create an Affiliate Program for your site?

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Let's hear from all of you that have created an Affiliate system for your site.

Did the cost of installing and maintaining the new software / code, the Effort of keeping the affiliates happy, the cost to pay them, and the struggle to create and maintain great offers & rewards, give you the increased sales that you had hoped for?

Better than you expected? Much worse? Or nothing really?

Now, it does depend on what you are selling, whether people will start snapping up all these chances to become affiliates and advertising your site, so when you post a reply, as much detail as possible would be greatly appreciated!