ARM doesn't mean "no fan". I can't wait for laptop fans to go away but currently the only fanless laptops you can buy are atom based and all of them outperform their ARM equivalents.
When you start getting into "laptop level" power (ie comparable to pentium), even at the ARM level, you start seeing fans. For example, the first generation nvidia shield.
No fan noise, no fan volume, no openings for dust to get inside the system. I personally can't wait until laptop fans go away.