I am no economist, so I don't understand how printing so much money, which should lead to inflation being rampant, has led to deflation, but that is where we are now.
I tend to see the current deflation as a 'good' deflation, as it comes from reductions in energy prices, meaning that people have more money in their pockets, but it won't help countries that are in debt as their debt increases with deflation, making it even less manageable than it is now (it already isn't manageble!)
I am no economist either....my guess is you print a lot of money and give it to someone who doesnt spend it
edit:fixed the wrong quoting
Roughly correct - the 'printed' money is actually composed of deposits held at the central bank. Although the owners of these deposits (other banks) could withdraw it and put it into circulation, they're being paid interest on it. The interest rate is very low, but it's risk-free so it's still a good deal from the depositors' point of view. Thus they keep the money locked up and the rest of the economy doesn't experience increased money circulation.