Supporting computer users by phone or email - is it effective?

We have come to the conclusion that the very idea of supporting users remotely, that is, via telephone or in any manner by which we do not have direct access to the computer in question, is ineffective. The networking and operating system components are so intertwined and dependent upon one another that in many cases we need to personally examine the computer itself to determine the cause of failure. We are now exploring alternate support models to address this need.