For one, the money pouring in is driving up prices. A pair of shoes that used to cost $20 now costs $50, for example. It also causes social problems with so many pirates using alcohol and drugs. "Teenagers threaten their parents that they will join the pirates if they don't get their way." How widespread and accepted is piracy? This quote says alot:
"The price of clothes, shoes and cosmetics is climbing, said Anshur Kamil, a businessman. Pirates don't even have to pay upfront. Those holding ships hostage that haven't yet received ransom can buy goods on credit — at elevated prices — and settle up their debts when the ransom money comes in, villagers say."
Can you imagine walking into a store and buying a pair of Gucci loafers and an Armani suit and telling the clerk "just put it on my tab, I'm good for it because I'm a pirate?" The article also implies that pirates are able to buy brides with their money.
Pirates have set up a stock exchange to find investors. See Somali sea gangs lure investors at pirate lair. This article was discussed at The Marginal Revolution.That article also mentions that it is not hard to attract young men to piracy since there are few legitimate economic opportunities in the area.
Economist Peter Leeson has written a book called The Invisible Hook: The Hidden Economics of Pirates.
Although the Somali pirates make millions of dollars, it still pales in comparison to what the movies make. Pirates of the Caribbean: At World's End took in about $960 million worldwide at the box office while costing about $150 million to make. Then it made about $295 million in DVD sales. And that was just one of the movies.