A feature that I miss a lot is the ability to group some columns under a title.

For example, let's say we have three columns labelled “Minimum temperature for this year”, “average temperature for this year” and “maximum temperature for this year”. It would be nice if you could state a first line of grouping labels with the text “this year's temperature” and, under that group, the three more readable labels “min”, “avg”, “max”. Something like: