depends on the reason why the guy is not driving. some popular reasons that i'd came across:
* that guy's a die hard environmentalist
* health/safety reasons like colorblindness, epliepsy
* some want to save money on other goals like buying a house, overseas travel, kids' education, etc.
* bad traffic, makes sense to ride on public transport
* that guy's under-confident to control a car
they are all valid reasons and are fine by me

although some people i know tend to associate them with "men of principles" and "men living in their own world" hence weird, difficult, or un-cool, which is bad generalisation, i think.
hence a similar question: what do you think of guys who drive cheapest cars money can buy vs guys won't drive anything less than mercs and jags?