Homebrew PCBs

Yes. I used them for a couple of years and even installed them in my Roland
plotter to plot circuit boards. They did an excellent job (if you were
lucky) and if the correct ink is used it is VERY resistant to etch. This was
my only method of making boards during that time. But then I got a laser
printer and abandoned the plotter and ink method in favor of toner transfer.
I would never go back and quite frankly I'm not sure why anyone is
considering going back to markers and technical pens when toner transfer
works so well. 

   The technical pens and plotter were simply a pain in the butt. I was
using the smallest ones available (0.3mm I believe) and they had to be taken
apart and cleaned after every use. There was an extremely fine wire inside
used as an ink release valve and it was sure to get bent when dis-assembled.
The pens required special cleaner to dissolve the ink. The pens frequently
skipped when used on copper (rather than paper as intended).

 For what it's worth Eagle can still generate plot files for the Roland
plotters but the plotters require a parallel port (rare these days) and
drivers for same AFAIK do not exist for the plotters any more.

 

 Forget the markers etc. and use toner transfer, it's cheap and easy.