Always feeling like I am missing out on cool stuff, I am using Slic3r cloned straight from development GitHub repository - https://github.com/alexrj/Slic3r

Today I found couple new notable features added:

3D path preview

This is just like in pronterface allows you to see layers in 3D. What is nice - it also shows different colors for different parts of the extrusion - i.e. it shows perimeters with one color, infill - with another and support with third color. Helps alot understanding what is going on. On top of it it also shows width of extrusion. All in all this is great feature which allows to analyze generated code for potential issues (too thin walls, gaps, etc)

This been said, layers preview is still there, but tab now called "Layers"

Infill/perimeters overlap

One feature missed in Slic3r was option to specify amount of overlap between perimeters and infill (Skeinforge has this feature.) Today I found this feature in latest master branch! Below is an example of 100% overlap - basically covers one whole inner perimeter (this is not practical I believe, this is just to show visually this feature).