Human factors can make playgrounds safe and fun.

This research is a great example of how human factors can be applied in a "fun" context.  What they did was study what factors of playground equipment is associated with injury risk and which factors are associated with fun.  Of course some things are both (high climbing bars) and some things are neither.  But they also found some things that are fun, but not dangerous.  So they created playground-design guidelines that are fun and safe at the same time.

Pretty cool stuff.