Hi Mark,
A quick question on this. I'm designing an updated version of the PCB and I'm wondering (for space reasons):
Does the de-coupling cap have to be only between the VCC and GND pin of the IC? In my application, I have +5V coming in to the area of the board with these ICs, and +5v is shared between two shift registers, and pullup resistors for 16 opto-isolator pins, plus anode supply for 13 opto-isolator inputs. I can probably guess what you're going to say, but I would much prefer to put one larger (0.1μF?) cap across the 5V+ and GND feed to this very tight area of the PCB if possible.
Here's a screen grab of my working design - I'm trying to keep it right to the bottom corner of the board, mirrored on both top and bottom planes. As you can see, it would be quite tricky to slip a cap in there to specifically cater for the VCC and GND pin of the shift registers (both in the centre)
