When a package is emerged, the archives are stored into /usr/portage/distfiles (cleaning this directory now and then may free up some disk space) but temporary files in the compilation process are located in /var/tmp/portage. Disk access is somewhat slower than memory access, so if you have spare ram memory, this trick is meant for you. Mounting a memory block on the portage temp area will speed up things for you.
For the purpose add the following line to you /etc/fstab file:


none /var/tmp/portage tmpfs size=2048M,nr_inodes=1M 0 0


In this case it’s a 2GB block, but you can suite to your needs. Please be aware that certain packages require HUGE amounts of memory, such as gcc, OpenOffice, etc…