I want to keep working while emerge is compiling stuff, but even with gentoo-sources preemptible etc. it still gets slow esp. with other process intensive tasks. I, for example, have to have a vmware working because of corel 10 and outlook + windows VPN + Office + Adobe Acrobat (not reader). (I could dual boot, I know). But having the update running unnoticed, using only the idle machine time, even if it takes 2x ~10x longer to compile is not a problem to me, and will not be a problem for many other users. I think there should be a setting in make.conf , defaulting to normal, but which the user can set to "low" or "idle", or even "high" if he wishes. Thanks for the attention.
Try PORTAGE_NICENESS