It's not very common. It was a great idea, but in reality, it only looks metallic when you print on gloss vinyl and don't laminate. Most of my customers that set up their printers with metallic ink have long since replaced it with a cleaning cartridge.
It would be more effective to print on a metallic substrate, but if you want non metallic elements would would need to print white ink under your color - but white ink is easier to find. Also, I've seen some pretty realistic metallic looking prints that are just created with CMYK inksets.
Good Luck
Joe