It should be noted that the hats that the new NPC creates for you are 'vanilla' i.e. any dyes that you may have applied are ignored.
My Dragon Mask is dyed black to suit my armour however when the NPC creates a copy the copy appears in its original undyed state; so don't delete your original hat if you've used an expensive dye on it.
Edit: Thanks - didn't see it mentioned elsewhere. Mods please delete.
Hats NPC: A Warning
Feanixxx
mega_jamie
This probably shudda gone in to the hat discussion, and it is already there and known about. Likewise runes will not be copied either.