After you have built your release WCF Service Library .dll in VS 2010, when deploying to IIS 7, the .dll file(s) should go under the bin folder of the application root of the web site.  This must be common knowledge, but it took me a few “bings” to find the answer from this link:

… As a precompiled .dll file located in the global assembly cache (GAC) or in the application’s \bin directory. Precompiled binaries are not updated until a new version of the class library is deployed.