*I'd much rather count in ones than in fives. On a grid, one square/hex = one unit of movement is intuitive, and even in theatre of the mind, I mostly think about how many 'steps' a character can take.
*Calling them "squares" or "hexes", though, is stupid. It yanks us out of the game world and into the real world.
*I'm all for metric in real life, but I think D&D should use more archaic units of measurement wherever possible. For that matter, I think it should use units of measure that are no longer common in the US, such as leagues for overland distance and stones for weight.
*That said, "yard" is both uninspiring and a bit on the short side compared to previous editions. I wish there was a unit of length about 4-6 feet long that could be used instead.
*Wikipedia informs me that the Romans used "pace" for a five-foot unit of measurement. It's meant to be a step with each foot rather than with just one, which is why it seems longer than what we'd think of as a pace today. I strongly support "pace" as the unit of measurement.