Recently, we've bought a pair of safety racks that attaches to the benchpress, and are easy to set.
With those, you never runs the risk of having serious incidents at contests, or when there are seriously heavy lifts in practice.
One of our best lifters had an injury to his ribcage due to the spotters, all four of them, not being alert.
Shit likes that pisses me off, but it's also inevitable.
And then, safety racks are lifesavers.
As far as regular spotting goes, the usual making sure a lifter can finish his set, I still believe it's the responisibility of the lifter to make sure the spotter is suited to handle the task.
YIP
Zack