There are a limitless number of ways to extend Zendesk, and SurveyGizmo, the maker of simple executable online surveys, has implemented a very cool use for Zendesk to automate their customer interaction workflow.
SurveyGizmo uses Zendesk for all their customer interactions by integrating a link to a customer feedback survey attached to notifications of tickets deemed solved.
Customers are able to give immediate feedback on the service experience, and by passing along customer and ticket information from Zendesk to SurveyGizmo, you can ask customers for only the relevant information and let the systems do the rest.
Read more on how SurveyGizmo is using the tool, and their tips for implementing it on their blog in the article Integrate Customer Feedback Surveys into Zendesk Solved Requests. Great stuff!