I would say slow walkers proliferate at around a rate of 3/10. You can spot them from 500 yards and if you're a fast walker you start at that point to make a strategy to not be delayed by them. sometimes however you get scuppered by 2 or even three slow walkers in close proximity, then you have problems.
I decided today that there is an absoloute minimum (i.e. it's not a relative thing) speed to walk and if you go below this it becomes annoying to pretty much anyone who wants to get anywhere in a reasonable time.
Once, I got stuck behing two people on the stairs at work walking excruciatingly slowly. I had to reduce my speed so much as I approached them (I hadn't spotted them at 500 yrds as there was no clear line of sight on this occasion) that it was noticable by people nearby. I can tell you now that these particular slow walkers should have been sacked for wasting company time, and if not that then they should have been horsewhipped simply for wasting valuable "living" time. My opinion is that anyone walking that slowly has A.) no respect for anyone on the same path as them and B.) far too much time on their hands and hence braindead (i.e. fill your time with something usefull. not just walking somewhere at zombie pace)... OK, you could argue they were walking and talking, they were, but as expected they were talkign rubbish and I believe that this woulkd be true of most slow walkers. Thinkers in my experience walk fast as they are usually exceited and keen to get to their desk/lab etc to try out whatever experiment/test/build/compile it is they have just contructed in their mind