Sounds pretty good to me. If I'm searching for a term, but don't want results from pintrest, then I'm probably not wanting to read an article about pintrest either.
"Here's a picture I took today. I also posted it on Instagram and Pintrest."
Except that the word "pinterest", like pinterest.* results, appears in all the nooks and crannies of the rest of the Web. Excluding the domain like that succeeds in narrowing the scope of the search without excluding content unduly.
If you wanted to read an article about Pinterest, it would probably be hard to search for it in any other way.