FWIW, I was able to export from Sketchup to OBJ using:
Wireframe OBJ importer:
http://moi3d.com/wiki/Resources#Obj23dmWireframe_converter

and I could make it Mac compatible by running the Wireframe OBJ Importer under WINE with the instructions at:
http://moi3d.com/forum/index.php?webtag=MOI&msg=5135.9

For those Mac users who are interested, here are the steps:

Find the drive_c folder in your MoI3d package and unzip so that there's a folder: drive_c:\Obj23dmWireframe
Put the .obj file you want to convert into the same folder.
After you launch the Command shell (see above instructions) you only need type:

C:\Obj23dmWireframe\Obj23dmWireframe to run the .exe. Just select the file and convert it. Then copy/paste the resulting file to your working directory. ***DON'T DRAG/DROP THE FILE AS IT WILL ONLY CREATE AN ALIAS!*** To move the file from the drive_c:\Obj23dmWireframe directory, just select it. Copy it (Command-C) then go to the folder you want to move and Option-Command-V to MOVE it there.

As some of you may have surmised. I only managed to drag/drop the alias and then MoI couldn't read the file :-) !!! HTH