Some more info he http://www.answers.com/topic/goubou-line

If you search for Goubou line AND Goubau line, you can find lots more.
Older editions of "Reference Data for Radio Engineers" had design info
on them.

The losses, as with any good line, are mainly due to I^2*R loss in the
wire. The current is lower than it would be for the same wire in coax,
for a given power, and thus the loss is lower. "YMMV" when it rains,
or when the line gets coated with soot and grime.

I believe I've seen it described as "quasi-TEM". Clearly if you look
immediately next to the wire, you'll find magnetic field symmetrically
encircling the wire, and electric field is always perpendicular to good
conductors so the electric field is radial. That's the same as in
coax, but if you look at the article Tom posted a reference to, you'll
see that the field lines do not remain perpendicular to the wire
further out.

Cheers,
Tom