For many years people built PCB's that successfully ran very fast circuits on two-layer boards. They built supercomputers, not to mention several generations of pretty fast DSP and video processing boards. It's possible, also, to build rubbish on a 4-layer or even 16-layer board.

Mike's board will run at 12 MHz (if he gets off the silly notion that becaus his oscillator seems to work at 18.432 MHz, he's "got it working" at that rate), which is not ultra-slow, but it's really operating at something like 1 MHz for most functions.

I've seen student-built boards that had no ground plane or power plane and were not too neatly hand-wired, yet worked quite solidly, often for long periods at a time without any hitches. I think it 's much less a matter of what's being built, and much more a matter of how. I've seen very terrible-looking combined analog, digital, and RF boards that had wires looping through the air, IC's soldered onto the board with only one or two pins touching the board, and lots of "spider-web" technology, yet they worked very well at frequencies well into the hundreds of MHz. It's all in knowing how to do it. The guys who know how to do that can design really good PCB's, too, but have convinced me that one can build circuits that work well on one or two layer boards with appropriate care.

RE