Thanks - I used Gnumeric on a netbook for a long time. It was indeed a good choice at a time when I needed something very lightweight. I do recall it being quite limited, however... I'd be pretty surprised if it had more of the features Joel Sposky was showcasing than Open/LibreOffice Calc.
It's been a year or two since I've used it, but the last time I checked, it hasn't improved all that much. It was generally rather slow and limited.
This is really a shame, because of Gnumeric's history. It was (along with Gimp) one of the very first GTK applications, and present at the beginning of the Gnome desktop suite.