Most bigger places or corporate places (like recruiting companies) do it as a matter of course. So do pretty much any retail job places. My little brother had to do a drug test before starting at Kinko's.
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.