If I don't misremember it's used by default for a long time, I think there is no need to ask people to: Parallel fetch When you are emerging a series of packages, Portage can fetch the source files for the next package in the list even while it is compiling another package, thus shortening compile times. To make use of this capability, add "parallel-fetch" to your FEATURES. Thanks Reproducible: Always
i'll mention that it's enabled by default, but it will still be documented, since the purpose of the guide is to talk about what all you can do with Portage. fixed in CVS.