Here is the first attempt at an addon to do an ‘inset polygon’ operation, optionally raising or lowering the inset polygon at the same time. It can operate either on individual polygons or groups of polygons treated as a single region (holes allowed). Insetting continues even after edges meet, in an intelligent way, using the straight skeleton algorithm.
Some example pictures are attached.
Please try it out and see what you think.
To install this, download the attached mesh_inset_01.zip.blend file and rename it to mesh_inset_01.zip, and then extract it in your addons directory (2.57/scripts/addons in the place where Blender is installed). Enable it (Mesh: Inset Polygon) in the User Preferences Addon panel.
To use it, go into edit mode and select some faces and then hit the ‘Inset’ button that is in the Tool panel. There will then be amount, height, and region properties that you can change. If ‘region’ is checked, it will inset the whole region - this will only work if the selected region is approximately flat.