I've seen a lot of talk on the interweb today about rusty chokes on some motherboards, and thought I'd weigh in with my 2 cents worth. First a quick description of what a choke does: the typical power phase on a motherboard consists of MOSFETs, a choke and a capacitor. The MOSFETs act as gates that open or shut to regulate the flow of electricity into the power phase. The choke acts as a battery of sorts that holds the charge while supplying electricity to the Capacitors. The Capacitors then regulate the amount of charge that the CPU (or other onboard component) gets. When the choke doesn't have enough charge left or it loses some of the charge due to EMI or other power loss, the MOSFETs have to open up and allow more electricity in. So basically good chokes hold a charge better than bad chokes, and therefore help reduce wasted electricity.
Enter the ferrite core choke: ferrite is that gray material that many fridge magnets are made from. It is better at holding a charge than iron and therefore it is generally accepted that ferrite core chokes are used on high quality motherboards. Another important benefit of ferrite is that it doesn't corrode like iron does. Rust inside a PC is something that you'll mainly find in coastal areas and it can occur when PCs are turned off and condensation takes pace as the motherboard cools down. As the chokes corrode, their ability to hold a charge reduces and they can eventually fail and cause damage to the CPU.