So far, I've used a user group policy object utilizing Internet Explorer maintenance to set a proxy for the user in IE. We have now deployed the Enterprise Client (EC) starter group policy to our domain and this policy affects this behavior.

The EC group policy uses the policy Make proxy settings per-machine (rather than per-user). This policy describes itself as:

This policy is intended to ensure that proxy settings apply uniformly to the same computer and do not vary from user to user.

Great! This seems to be an improvement over my previous setup.

If you enable this policy, users cannot set user-specific proxy settings. They must use the zones created for all users of the computer.

What zones and where do I configure the proxy settings for them?

I assumed the policy would simply take the user settings and apply them, but that's not what's happening. Now no proxy server is set at all. So my previous settings obviously no longer have any effect.

So far, I've only come up with solutions that involved direct manipulation of the Windows registry. Which is fine, I guess, but the way the proxy is configured for users makes it appear as if there could be a higher level approach.