It's good that you're ready to embarrass yourself, I am too. They are hard to build, because of decoherence as you mentioned. They also are more suited to parallel processing than sequential processing, which is what I think you're getting at. Quantum computers solve BQP problems efficiently while classical computers solve BPP problems efficiently, if you want to sound smart.
Quantum computers use the phenomenon of quantum entanglement. It's possible to entangle two quantum particles so that certain states on one particle (or qubit), such as spin, affect the state of the other qubit.
You know how logic gates work, right? The NOT SEXP and the AND SEXP? Well let's say two qubits are entangled so that qubit A always has the opposite spin of qubit B. So if qubit B is manipulated to have an up spin, A will have a down spin. We've just made a NOT logic gate.
Now say that qubit C is entangled with both in such a way that it will only display an up spin if both D and E display an up spin. That's an AND logic gate. And so on, recreating the entire series of logic gates that exist in any other processor.
The great thing about quantum computing is that each qubit may be entangled with every other qubit in the processor at the same time, so you can perform exponentially greater operations if you can increase the number of qubits entangled with each other. Basically, infinite money. Exponential versus linear. Although everything's log, really, if you take it far enough.
However, if you were to write a program for the quantum computer, it would have to wait for each gate to complete its current operation before proceeding to the next step. So one should always try to construct the problem in a way that allows parallel processing to get the most juice out of each step when writing code for these machines. But the high speed of data transmission between qubits (near instantaneous) and the exponentially increasing parallel capabilities with each additional qubit makes these computers a whole lot more effective than classical computers for most problems if the programmer isn't an idiot.