As a modo user, I attest to its fantastic fluid behavior and swell interface. Great "usability," as the current human/computer interface jargon goes.
Best example of modo use here in Vancouver [the Embassy]:
http://www.luxology.com/article/113004_1/1.aspx
worth waiting for the download.
My personal favorite for cool interfaces however, remains LightWave - a sophisticated modeler/renderer for use in architecture and cinema - also popular in a swank deep-thinking subculture:
www.newtek.com
ArchiCAD could certainly be sent to the cyber nip/tuck guys for an interface redo - liposuction, re-integration, dermabrasion and a dialog box tuck.
Dwight Atkinson