In our code, we make the
System.Net.IWebProxy xProxy = System.Net.GlobalProxySelection.Select;

This, in all our testing, gets the proxy setup for use in IE.

However, a customer is experiencing a situation where their IE proxy is
setup, but that call returns an empty proxy. We've worked around the
pressing issue, but it leaves me wondering what the call above is
actually retrieving? Is it possible that this doesn't get the right
thing if the proxy is setup differently somehow in IE?

I've also seen talk about WebProxy.GetDefaultProxy() ... we have yet to
try this with the specific customer, but does anyone know exactly what
the differences are between the two calls?

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