They work a little bit. I went to a psychic in my local town and I randomly chose some upside down cards. She looked at the ones I picked and explained how each one is relevant to me and my life. Some things I already new about myself, but some where surprising. I don't know, I am still skeptical about it.
It will be most accurate telling you the present and the influences around you. The future however is if nothing changes, but you can act to influence this if you want to.
Sometimes. And sometimes the cards tell you a bunch of crap. Sometimes they are talking about one of your friends instead of you. Sometimes they are talking about the plot of a TV show you'll be watching tonight. The more often you ask them, the more full of pranks they become.