I have been creating these gem forms in Rhino for a couple days now by hand... Starting with a profile curve, extruding a small girdle, creating a duplicate edge of the girdle and then extruding that curve to a point...
The forms are turning out relatively nice - I'm getting interesting facets but they aren't true gem forms as both sides are the same.
I was browsing through the RhinoGold tool panel and noticed the Gem Creator tool and decided to give it a try. All this tool requires is the outline curve to create the gem shape and from there you are just selecting options on a tool panel. It significantly reduces the time spent modeling. This tool is a definite win.
Below you can see the gray gems are the ones I've created by hand, and the black were created by the Gem Creator tool.
I appreciate the ability to easily achieve consistency in the Gem Creator - You can also save your gems to a library to use them with other functions like the array and channel commands. I can definitely envision myself using this tool a lot in the future in jewelry to create and utilize custom stones/forms.