Any of you every learn a 2nd language? What worked for you?

My wife's cousin live in France and we had sent them Rosetta Stone English version to help their two children learn English at home.
In two years they learned enough to communicate with my son while visiting us. They spent three days at Disney World talking up a storm all in English. I was very surprised.

Thanks for all the feedback so far.

working with Cubans and Puerto Ricans, I learned the cuss words, bodily functions, where does it hurt,open the door and put your hands up. basicly enough to get drunk,laid and in a fight. what more could you possibly need?

I can by drinks, get a meal and get in trouble with young ladies in about 12 different languages.
I didn't need Rosetta Stone to learn all those language.