There is no "foil ink," just metallic ink! I have seen gold foil used on at least one deck, but the process for using it is not simple by any means. Don't ask which deck - it's not in release. It's used far more often on tuck boxes.
Most designers really drop the ball when it comes to metallic inks, gold in particular. Gold ink NEVER looks as shiny on pasteboard as it does on your monitor. It really is more of a mustard yellow-brown, like Gulden's Deli-Style mustard. It's actually somewhat dark, and shows up best when displayed against a light or white background. Silver can work better on dark backgrounds, though it, too, is never as shiny on the card as on the screen. Silver on white can be hard to distinguish - Lance Miller's Bicycle Gargoyles is a beautiful deck but in the wrong light becomes utterly unreadable, the metallic silver ink having a nearly-identical reflectivity to the white background of the pasteboard.
Metallic inks I think are better used in more subtle ways. The best example that comes to mind is the Sliver Split Spades. Now, we've all seen decks with metallic red ink for the reds, but it always looked odd to me when the blacks are done in black ink, totally flat and lifeless in comparison. But Mark Stutzman made a fantastic choice in doing what appears to be overprinting the black pips with a scattering of gold ink. Suddenly the black cards aren't so flat and lifeless anymore. It was an inspired idea, really. The backs being all silver on white makes them a little tough to see in bright light, but they're the backs, so one doesn't worry so much about it when using such a deck.
And I think that's enough from me on the topic of metallic inks!