For those of us who use gentoo as a desktop PC and frequently update, it would be welcome to have an option to have the usage of 'nice' turned on by default. (memory jogger) 'nice' makes a process run with a lower priority so there is little impact on system performance. 'nice emerge x' (including nice emerge sync) allows the system to remain responsive.
Although not directly what you are looking for, you can make a system-wide function for emerge: emerge() { /usr/bin/nice /usr/bin/emerge $* 5 } or something like that (bashscripting isn't my best point :)
kernels 2.5.65 and later will kill this... it'll be invalid by 2.6 so I'd mark it invalid now.
This has already been taken care of. Look at bug 18868.
It's in make.conf. PORTAGE_NICENESS