Absolutely yes. Client NDA's are quite common, so just send me the paper work, and I'll scribble my signature on it. However, I always like to be able to show any finished work in my portfolio, once the project is completely finished. If the NDA prohibits me from displaying the work I've done for a client, for all eternity, then sometimes I'll politely turn down the project. My portfolio is my window front and the way I hook in new clients, so if I'm not able to show the world the one thing I'm very good at, then this isn't good for my own business.