A Simple Guide to Creating Heatmaps (blog.smartbear.com)

Also, the QGIS heatmap plugin is very good and fairly simple to use (although, admittedly, it's a little more involved than OpenHeatMap).

I didn't realise that gMaps now had a heatmap layer option. That makes life a lot easier for me (once I work out how best to bucket the points into WeightedLocations).

I love that he used brony data for the examples. :-)