Hi Michael, cool update!
I have a few comments regarding different things :
* It looks like you have choose a right handed system which is a good thing. You should make the XYZ directions more obvious, maybe a subtle hue change (RGB) in the grid...Another thing is the fact that you have choose Z as the "vertical" which is not the most used convention in the entertainment field. If I open an obj export in modo or maya ( right handed but Y up by default ) I must rotate 90 counterclockwise around the x axis to work in the same space. I think you should provide a little bit of matrix manipulations options for the exporter like in Zbrush for example ( there's a lots of different pipelines around !).
BTW you should change the icon for the rotate axis command ( Left handed ! ), this can be very confusing for some artists!
There's also some scale issues. If I open the file ( I have set meters as the unit ) in modo no problems but in maya which is in centimeters by default ( not sure how maya deals with obj ...) I get 1 meter = 1 centimeter...So you must provide a multiply just to be safe for all the cases.
*The grid could be more useful. I like the grid snap (discrete values space) feature and it would be cool to have a multiply field for the snap size value based on the zoom/distance camera to grid. This way the grid would become more "adaptative". Of course a toggle is needed for this feature to lock the grid when needed. Also it would be cool to display the current snap size value ( after the multiply ) near the world space coordinates tracking system ( based on this adaptative grid feature ).
*about transformations in the 3d view : at the moment if I translate for example some points while being mostly facing the grid ( XY plane ) no problem I get what I expect ( moving in the XY plane ). Now, in a more "fresnel" type of situation I have a problem if I try to translate my points. You really need to allow the user to move in the other planes in the 3d view ( amapi comes to mind ) as well as the screen space too if you want to please the artists! This is really important. Having a visual feedback for that is really good too.
*Be sure to give us the "complete" orientation (not just one direction/1 vector ) the day you deal with orientation tools this is really important! BTW I love the fact that we can extract points now, all the information we need is here ( ...define a vector, a plane, a direction, a new coordinate system...)!
*about history: I have try to build a surface based on 4 curves. I can tweak the curve after the fact but as soon as I edit the control points for the surface I loose the history. It would be really cool to have 2 levels.
*shear and taper are the more useful for hard surface modeling...Now if you could provide different type of interpolation ( not just linear ) for those deformations that would be really nice.
I will send you an eps file from modo....I must check that.
Very popular plugs for lightwave ( just to give you some ideas ) :
http://www.pictrix.jp/lw/index_1.html
Hope this help.