The wear is only part of the
problem, the cam follower is teflon coated and can over time wear through entirely which means you can have bits of the metal casing floating around your engine. The worse resulting damage can occur when the cam shaft lobe is worn and damaged as a result of the cam follower wearing out prematurely.
Several cars in the US had to have new camshafts fitted as a result of the issue, in the states they did a recall on the engine. This is the biggest
problem, and some of the later engines were unaffected, though the cam follower still shows wear, the cam-shaft lobe is harder and less likely to be damaged.
The issue is really one of occasional maintenance, the part does wear, its teflon coating is designed to lessen wear over time. But the lifetime of the coating has been over-estimated it appears. So its worth inspecting occasionally, and any signs of excessive wear through the teflon coating the cam bucket follower should be replaced at the earliest chance.
For the sake of a £25+ part once every 20k miles or so, has to be worth it, to save a very costly engine repair bill.
Its certainly rare, on the later than 05 engines, but it doesn't mean preventative measures should be ignored.
Seals on the replacement pump internal kits seem to be more problematic though, than this initial
problem.