Version 2.1 is here!
This script creates a bevel in the shape of the selection. The script appears as Filters > Distorts > Bevel. The bevel is created on it's own layer. You can adjust various things, like width, azimuth (light angle), etc.
Comments and feedback are welcome.
When you download the script, you have to rename it so that the extension is ".py" and not ".py.txt", otherwise it will not work in GIMP.