For a recent project I was conducting some fairly dry quality assurance/quality control. In particular, I was comparing whether the population-weighted centroids of ZIP codes (ZCTA, to be specific) we computed in PostGIS matched those computed using QGIS. Given that I was creating temporary, internal maps, to make things more fun, I used the OpenLayers plugin to add a different kind of baselayer. Instead of using Google/Bing/OpenStreetMap I used Stamen Design’s watercolor baselayer.
The resulting maps are a crazy-quilt of color but brighten up an otherwise relatively dull GIS 101 task. And look the centroids match (see the big circles with the little circles inside).
New York City area
Small circles color-coded by ZIP code and the two central circles (one bigger and one smaller) are the population weighted centroids computed using PostGIS and QGIS, respectively.