Only time I've ever had to take a pre-employment drug screening was for a summer job at a storm door factory. Made sense there because I was going to be working with heavy industrial machinery.
I'd have a problem with taking one for a retail or office-type job. It's the principle of the thing.
I wouldn't be surprised if there were state laws about it for companies with over a certain number of employees. In states like CA, I mean.
Not saying it makes sense...just sayin' is all.