Puller fans are more efficient on the order of 18-20% based on what I've read, much as Gilby has said, a pusher fan physically blocks the radiator surface and that accounts for a fair amount of the difference. A good puller fan will be shrouded and thus pull air through virtually the entire core, an unshrouded puller or any pusher (which cannot be shrouded) are automatically less efficient due to this.
This is a good example of a shrouded puller
http://earchitect.50megs.com/Elcamino/images/engine/DSCF1391.JPG
When those fans are running they pull through the entire core without blocking any of the core from the front.
As for your safety drop off, those guys need to get out more often, there is nothing terribly uncommon about pusher fans, its just that they tend to be used as backup fans, not for primary cooling.