The biggest myth is probably that the CPU is the most important part for performance. There are so many other bottlenecks that you can easily run into (drive, memory, memory bus, ...) that blindly updating the CPU (more MHz / more cores) is simply wrong.
I think it's pretty incredible to see our processors finally catch up and overtake our computing requirements. If you have a first-gen i5, or even a Core 2 Duo, your CPU is plenty fast to complete 99% of computer tasks out there without feeling any sluggishness. 10 years ago, when people would come to me for advice on purchasing a laptop/desktop, I would tell them to buy the best processor they can afford and then upgrade the rest of the components while they use it. Nowadays, most decent laptops ship with an i5 at minimum, some people ask me if they should upgrade to the i7. I always tell them to save their money and spend it on a faster SSD or more ram (if the ram is <4gb).
The biggest improvement on current laptop for me is SSD. Man that's biggest jump in performance (perceptive) in a long while.