I had to quit doing so, because I discovered that it didn't just exclude listed domains, but performed a totally different search. Locations or local results were largely missing, when I excluded some domains.
Or did it just have to perform a non-cached search and thus not only excluded said domains, but could also reorder the other results based on the current relevance, rather than cached relevance from the past that is being served to everyone else who doesn't exclude said domains?
PS: I'm blocking all ads.