So this should mean that a 2MHz CPU is twice as fast as a 1Mhz CPU right?
Well, unfortunately it's not quite that simple, because it depends on how much work each CPU accomplishes in each clock cycle.
The 1MHz CPU might even be faster in some situations than the 2Mhz CPU - if it is more efficient or can process more tasks in each CPU cycle.
CPU speed is not the only indicator of CPU performance, although it is probably a reasonably indicator for most of us when buying a new PC.
Remember that factors inside and outside of the CPU have an impact on CPU performance, and on overall speed of your computer. These might include a slow hard disk, not enough RAM, a slow graphics card, etc.
These days even budget laptops will have a CPU around 2.0GHz speed.
Desktop computers might have CPUs around 2.5GHz to 3.0GHz.
Generally only a network server requires CPUs that are higher than 3.0GHz.