1. I coulnd't flip my object in the object properties window, as in mirroring the object by putting a (-) in front of a scale axis value. Considering this is a standard in all 3D softwares, so why not in simplify3D as well? Please enlighten me if I'm missing something here.
2. Horizontal slicing and printing a section of an object should also be an option available in the object properties window. I know there is an option for it in one of the FFF settings, but it sounds more logical to enter this setting in the object properties window. This together with a preview of the sliced 3D object in the viewport would be nice.
3. Custom grid spacing has already been mentioned, but I would really love to see this, so the grid would give an matching representation of the size.
4. I would also love to control the printing speed for infill, separately from the default print speed. My printer will shake like crazy when I print thin (not single) walled objects, and I will have to turn the default printing speed to way low to avoid the shaking. You have outline underspeed, and you have support underspeed. Why not just add a similar option for infill?
5. Not a big deal for me, but I used to be a fan of the acceleration feature from Repetier Host. It might be a huge task to implement a such feature, but I often experienced a nicer corners, especially those with a sharp U- turn. This also helps when printing objects which have islands in the start.
Just my 0.02, other than that, I love the software, and would't go back to any other software any time soon. But I feel having these features really would provide simplify3d to become an even better printing software.