Coloring the word "ignore" with a darker color when a user is ignored by many people.
I dont see how such a small error can make such a big difference.
If the feature was written as:
-For every thread page of 20 posts that someone views:
-for every user that posted:
-look through every other user's ignore list and add up the times that user has been ignored
it certainly could cause server load. If it comes back, it would probably not be a "live" statistic, but one that is compiled nightly per-user.