I am constantly chipping fan blades (gone through about 3 replacements).
Garyacrowellsr's fan guard is great, however since i have to remove it before i unscrew the fan, it doesn't protect against the situation that has killed most of my fans! (namely, accidentally jamming a allen wrench in there when i am doing a quick cleaning job).
This version is split, and features screw holes, so it can basically live on the fan without ever being taken off.
Plus, along with http://www.thingiverse.com/thing:28241, the extruder kinda looks like a face.
Also refactored the original scad source to be a little easier to modify
Print with default replicator settings, and just slide it down over the top of the fan. Boom, done.