Google referrals only- we are currently in a busy zombie period, and about 20% of referrals are zombie. "Normal" is more like 5%.
We're lucky in that our zombie traffic just does not impact our normal transaction rate. It often ramps up before and during some kind of major shake-up. We normally sail through those changes with little impact, but the pain is reflected in the general outrage seen from some quarters in other threads.
To be fair, I didn't beleive in traffic shaping until one product started stealing other referrals- I've never seen a buzz-cut line that is the classic (if rare) report. And I didn't believe in zombies until we modelled it.
In a way, "Zombie" is an unnecessary personification. Until the last year or so, we just left it unanalysed, as temporary unfocussed traffic during an major or minor update. We assumed it was the algo honing its query/user intent matching by website. So we just accepted the additional traffic, higher bounce rate and lower conversion rate. It was temporary, uninteresting and non-impactful.
Its only since we started trying to extract more revenue from the blips that the low-level persistance, the evolution (it slowly ramps up, and usually rapidly falls at the macroscopic level) and the total failure to engage made it more interesting.