Today's upgrade of openssl to 1.0.2g-r1 may cause some necessary rebuilds to fail due to missing symbol errors.
Example: libcurl was broken and caused the rebuilds of virtualbox and git to fail until I forced a rebuild of curl. Any installed package that is actually linked against openssl will be affected by this, notably curl or wget, which may prevent portage from fetching source files. I suggest using quickpkg to back up openssl before the upgrade in case you need to recover urgently in the middle of the update.