I work in the manufacturing industry, so walking around in 4" heels usually catches some stares. I have a ton of them...but rarely wear them.
And, to answer your questions.....they are "moderately" comfy. You won't find me out running errands in them....but I can wear them the whole day here at the office, and not spend my time wishing to be put out of my misery.
I've been walking around the office, to and from my car (etc) all day today. But when I ran to a store over lunch, I switched into a pair of black sandals. Any time I can reduce the stress on my feet, I try to.
I could totally get rid of the stress by not wearing the shoes at all...but what fun would that be???