Measuring web sites and online marketing campaigns has kept marketers, agencies, and others busy for years. Web analytics report visits, page views, visits and other counts of site activity. Ad server analytics report impressions served, clickthroughs and other silo-specific measures. Once upon a time, each delivered the "hot metric." But, as soon as we begin to understand what each "hot metric" tells us, we begin to understand where it falls short, and we begin again to search for the "Golden Metric" that we can confidently use.