This parameterised script creates a circular bowl whose profile is a super-ellipse. http://en.wikipedia.org/wiki/Superellipse. I use the parametric equations in the script.

You can change the radius, the height, the wall thickness and the shape of the superellipse by varying p: 2 would be round, 2.5 is Piet Hein's superellipse and 4 a Squircle

I've not printed it yet - I guess it would be OK printed upside-down

more on its development in my blog http://kitwallace.co.uk/Blog/item/2013-02-14T00:10:00Z