Laser for PCB Prototyping?

I've had a great time working on circuit designs in Eagle the last week or so-- after my surgery, my sciatic pain is mostly gone and I'm able to concentrate again! Still, I'm mostly confined to the neighborhood and can't lift or bend or exert myself for another few weeks, so I'm happily plugging away at a few projects, the main one of which is my latest coffee grinder timer.

The timer PCB's odd shape was dictated by the enclosure's design, resulting in a 100mm x 74mm board. It needed to be double-sided, but traces were made wide and vias were kept to a minimum in the interest of home prototyping. I've had great success with toner transfer in the past, but not for 2-sided boards, and not for anything large.

A PCB-production process I've wondered about is using a laser engraver to remove an etch-resistant layer on copper before normal etching. The best and most successful example I've found is on Instructables: "Custom PCB Prototyping using a Laser Cutter," where the author uses flat black Krylon indoor/outdoor paint as the resist.

The example (at right) shows a single-sided board, but I'm primarily interested in using the process for excellent top-bottom registration. Before attempting the large board, I will first try some small pieces with test shapes, then I'll try a double-sided ATmega32u4 breakout board (my own design), then Grinder Timer 5. Stay tuned...