From my experience, most people (including me) will not notice a 3.6. I do note a 4.2 (which is 4 times stronger) but some people do not. A 5.2 seems to be noticed by everyone and a 5.8 (like the earth in VA that shook the eastern US in 2011) is scary. Every .3 increase is a doubling in magnitude and a 1.0 increase is an increase in 10 times the magnitude.