I've developed a new OBJ exporter for AC3D. All the features of the existing AC3D export, but adds groups, lines, textures, and optional copying of textures to the OBJ output directory.
Windows-only, but source is included if you can (or know someone who can) compile it for other platforms.
Find it here:
http://supercoldmilk.com/ac3dplug/objenh.html
See all of my plugins at
http://supercoldmilk.com/ac3dplug/index.html
Enjoy