Profiling data in PowerPivot: comparing two tables

On a prior post, I described the process in which one could use PowerPivot to find duplicates when exploring a dataset. Another common scenario when first diving into new data is finding common records across two different tables.
Level: Easy
Problem: You have two datasets and want to compare attribute values across them. In concrete terms, you want to understand if a particular key value is present in the other dataset or not.