The aluminum body transfers heat more effectively than other materials used in computer casings, so you will feel the heat more. It is also quite normal for your Mac to become extremely hot to the touch during intensive operations. It's just your Mac doing its job to maintain temps within the normal range. If you're constantly putting high demands on your system, such as gaming or other multimedia tasks, expect temps to rise and fans to spin up accordingly. Websites with Flash content, games and other multimedia apps will put higher demand on the CPU/GPU, generating more heat. Unless there is a rare defect in a Mac, most temps are well within the normal operating range, considering the workload being put on it. iStat Pro will give you accurate readings of your temps and fan speeds, among other things. The Intel processors used in Macs are designed to automatically shut down to prevent damage if they truly overheat (around 100C/212F - 105C/221F, depending on your processor).

Click to expand.Any fan control software that limits the maximum fan speed is not recommended, as it can cause overheating.

Windows fan control software