The Mortimer Trap is one of my favourite traps. It is very easy to learn and since the Ruy Lopez is so common, players have many opportunities to try it out. Watch out for the smothered mate in the alternate line shown here.
In a game I played a few days ago, I baited White into the Mortimer trap but in the Italian Game rather than than the Ruy Lopez. First I offered him my pawn, after he captured it I followed through with the trap. It actually worked, just have to remember that White has to close his pawn chain. If your opponent knows the trap; than you'll be down a Pawn.