I've had one person on my ignore list, but just removed him because hasn't been posting lately. It's not about equilibrium as much as S/N ratio -- some people combine very high volume with very low value per message, so I ignore them. Fortunately this is very rare indeed here.
I've occasionally put someone temporarily on one, if I've found myself getting inordinately irritated by them; this happens rather rarely, though. The trouble is that this forum makes it too easy to peek, and if I'm irritated, the temptation to peek is very high.
It does raise the threshold of shooting back irritated replies, though, which is a good thing. Publicly announcing that "I'm ignoring X" will certainly raise that threshold further, even though it's a wee bit too kiddies-in-a-sandbox for my taste.
Back in Usenet days, plonk and follow lists were a necessity, though -- in a high-volume newsgroup, it would be impossible to find the signal among the noise without them.