I'd also like to add something about the feathering.

There are actually two types of feathering in Xara Xtreme - Graduated transparency and feathering control.

The closest you can get to what you're example shows is to have an eliptical graduated transparency. Not great for anything other than elipses though.

Uses? Plenty I can see. Vingetting, edge masking and other framing techniques.

What I would like to see in the feathering control (and this would provide what you're looking for too!) would be a way to select which edges get feathered (inner, outer, this half, that half etc). One could add control points to limit the effect precisely. This would provide the facility to partially feather a polygon which would be fantastic for photo composition, motion effects and probably loads of other things (not to mention shadows and highlights).