They don't work 100% of the time for various reasons, but I've found they work quite well the vast majority of the time.
Of course, it's not like Bewitched. You have to be realistic in your expectations, work with the way things happen naturally, and most often you have to do the footwork to help it along. For example, if you're unemployed and do a money spell it's not likely that it's going to work if you just sit on your butt and wait for the money to roll in. For the best results you should start looking for a job, and at very least you might want to buy a lottery ticket. Not that you're likely to win the jackpot, but you may just win a few dollars to help you along.