Does HDV = 4:2:2 SD?
I've seen various technical discussions on this which go right over my head, but I want to know, if I downconvert 1080i HDV to a 4:2:2 SD codec like DVcPro 50 or Canopus, will I get full 4:2:2 colour from th FX1 in standard def?

Pretty much: effectively HDV stores the color information for a group of four pixels, and when you scale down to SD from 1080i you're cutting the pixel count by about 75%. So absent compression issues, you'll actually have more color information than shooting native 4:2:2 SD; a smart scaler could probably use the extra luminance information to give you ten-bit video as well.

The next question is, would the same apply to an FX1 or Z1 shooting in DV mode?

Or is it the ability to just pull more info out of a HDV image?

Thanks for the reply Mark. I thought it was something like that given the amount of info on 1080i. Some of the tech discussion are v complicated.

The next question is, would the same apply to an FX1 or Z1 shooting in DV mode?

No. DV25 is always 4:1:1 or 4:2:0.