I do this but clarify what the interview process is like as a first step to communicating with a company. As soon as they state this as their intention I tell them I'm not interested. I've been hired at places anyways. My personal opinion is that I have enough projects, years of experience getting a paycheck each week and GitHub/Stack Overflow contributions to verify I at least have a grasp of what it takes to be a web programmer. I refuse the white board exercises outright. I won't do large homework assignments either.