In reply to thelostjockey:
I have MN in both feet, bot badly enough for surgery (thankfully). Custom-made NHS orthotics helped a lot - I wear them when walking in boots or approach shoes and when running. I still get some pain, and it's difficult to sort out the right balance of socks and orthotics (because orthotix take up space so socks can cause over-crowding). As said further up, any tightness across the arch causes pain.
When last MN was discussed on here, someone swore by separating the third and fourth toes. Coincidentally I tried that for the first time today, on a 10-mile walk up and down Dunkery Beacon. I had a comfortable day without the usual bout of pain after a few miles.
Lizzie