Prata does say to "avoid" using DIRECTIVES in header files, but even there, he doesn't make it sound quite as taboo as you are suggesting...
In large code bases it is extremely taboo. Others who include your header bring in the entire namespace you brought into the header. In a cpp it's perfectly valid to use a using because your implementation file will not be included by anyone else - providing you have at least halfway intelligent programmers on your team. If someone does include your implementation file and it's not a template impl then you can smack them for being stupid.