We still send the kids with a cough or runny nose to school, playdates etc. Fever, diarrhea, vomiting = 24hrs free of all symptoms before they leave the house again in my book.
My kids were sick so much their first few years of school as they built up their immune systems, and if I kept them home for every cough and runny nose....they probably would have been home 1/2 the year
But, anything worse than that they stay home.
Pinkeye is supposedly not contagious after 24hrs of treatment, so I send them out after the 24 hrs. Also, for a lot of rashes, they are no longer contagious after the rash shows. So, I try not to judge to harshly when I see kids out in public like that because the parents could very well be in the right.