I'm picturing steam coming out of Dr. Anderson's ears, but also a broad smile, because he thinks to have managed to make the scheduler appear simple, yet it being under the hood quite complicated.

No the idea is not original and adds another layer which for many could reprisent another layer of confusion. It was entered on the wish list though at the Berkeley developers forum.

You can set BOINC to only crunch when the PC does not receive input from keyboard or mouse for X minutes. I think that at the end of the day it generates more used CPU idle time than a 90 / 20 as you'll have to decide what the 20% period is.

But, most importantly, 20% is impossible noticed by a user, not even 50 or 75%, were it not that the hack saw throttle build into BOINC, and now Dr. is clenching his teeth, runs with a 20% setting in the pace of 1 second at 100% and pausing 4. Now people, particular on slower systems do notice that.

If on windows, the superior control is ThreadMaster+Threadmaster GUI (See Start Here forum FAQ) as the alternate. Set the percentage to a level that you wont notice during use time.... very smooth.