One of the first things it seems like every interested hacker asks me about the Cricut is, "how can we get it to do PCBs?" Well, I've finally done it!
I created a single-sided circuit design in Eagle, using 50 mil traces, then exported just the pads and traces as a monochrome PNG file.
Next, I sprayed a coat of clear spraypaint on some single-sided 0.01" PCB material and let it dry well. (Next time I will use two coats)
Finally, I imported my design into MTC using pixel trace and used my scribing tool to scratch the design onto the PCB (multicut 2, pressure high). This removed the spray paint around the edges of my traces. After it was done, I used a toothbrush to brush the removed-paint-bits off the board.
Finally, I etched with a few tablespoons of ferric chloride in a double-bagged-ziplock immersed in hot water. The whole etching process took less than ten minutes. Aside from some unwanted specks where my one coat of spray paint was a bit light, the result looks perfect!
Obviously I still have to do more work to make this board functional, I'll report back when I have more to show.
EDIT 3/13: I tried drilling the board and soldering up one of the oscillators, and it turned out that there were a couple of shorts in my etched diagonal lines where some "jaggies" were really close together. Also I discovered that the "donuts" need to be larger in diameter to leave more solder pad remaining after drilling the hole, especially the ones for the 555 chip.