For me, working with one of the first quad core systems was amazing. No matter how many applications you run at the same time, the system reacts to user commands quickly. Some applications require half the time to finish tasks. To me, it's like being catapulted a year into the future and is unlike the past few years when computing power increased only marginally. Intel pumped out 30% more performance with Core 2 Duo and will double that again with Core 2 Quadro soon.
Source:Intel's Core 2 Quadro Kentsfield: Four Cores on a Rampage