Whilst the theory has been known for a while building a real Practical working quantum computer has been impossible until recently.
Without going into quantum theory too much these computers work on the basis that instead of a bit that can be '0' or '1' a "qubit" can be BOTH at the same time.
The problem of course is in reading the values as any attempt to measure the values directly "change it's state" and cause degradation in the qubit.
The theory shows that say you want to decrypt say a DES encrypted algorithm. With classical computers even with the fastes Crays around testing all possible combinations would take many times longer than the expected life of the universe.
However with a Quantum Computer you can run ALL POSSIBLE COMBINATIONS AT ONCE (or at least for as many qubits as you have in the machine).
This will kill of cryptography as we know it -- maybe a bit of overkill to rid us of music DRM .
Here's a link to a nice piece of "Bed time Reading" for you HowStuffWorks "How Quantum Computers Work"
and another Category:Introductory Tutorials - Quantiki | Quantum information wiki and portal
Now off to another problem -- seeing Manchester United copy Liverpool and get a few goals tonight.
One of the 2 great inventions to come out of the UK.
2) Football (the real kind where people actually have to KICK the ball and it's a round ball not a squashed rugby ball with players wearing padding that makes them look like "The Michelin Man").