Keeping your PC up to date is expensive, which is why most of us choose to build a new PC at a specific point in time. Throughout its lifetime, we may perform CPU, GPU and RAM upgrades, but at a certain point we decide that it's time to start completely fresh with a brand new box.
At which point do you decide that it's time for an upgrade, either a full overhaul or just a simple drop in/swap part?
In other words, for our QOTD, we'd like to know from you exactly what determines your upgrade cycle?