As best I understand the discussion in #wikimedia-tech last night, ~20% of search server load was being taken by aforementioned spamvertisers. That sounds like an "urgent production impact" to me.
50% of load, which at that time was using ~20% of search server CPU load. It also cut our API node traffic into half (some CPU too), and got our average response times for API way nicer: http://www.nedworks.org/~mark/reqstats/svctimestats-daily.png ;-) Also it removed some pressure on API squids, which were misbehaving yesterday, and caused API outage.
Also, currently 20% of cluster CPU is being spent on generating atom feeds for people who never really subscribed to them. We don't know why, yet, though :)
Domas