Can one cx or cref ID be used to call Google custom search across multiple API keys?

I'm investigating the Google custom search API and I'm a bit confused about how to go about it.

I've been scraping google.com?q=my+search+phrase in my app and it works great. However, I want to use the custom API to stay compliant with Google TOS, so I'm looking to port my app to the custom search API.

Assuming that my app will ship commercially, and the end user will be required to obtain an API key themselves (which the app will feed in as a variable before doing an ajax/rest data call), is there a general cx or cref ID that can be used across all API clients?

Or, does each client have to obtain their own unique cx or cref ID as well?

I want to make it as simple as possible on the end user. All these IDs and APIs will become an issue for less开发者_C百科 technical users.

The sole purpose of my app is to pull the top 10 organic URLs for any given search.

CS is unique id, see http://code.google.com/apis/customsearch/v1/using_rest.html#cx

You can find it at your customer search control panel, right above "save changes" button.