I never have had a piece of metal stuck in my eye, but I always wear safety glasses.A lso, when ever I am using a grinder, I wear a face shield since one time while using a grinder someone put a 7" wheel on a 4" grinder (that was worn down) and the wheel shattered. It kinda scared some sense into me, that and the 7 stiches in my hand.
At the time I was taking a OSHA 30hr. class for my shop steward cert.(carpenters union). The previous saturday, we discussed the very same thing happening.
Needless to say, when I went back for the next class that saturday and the instructor asked what happened, I felt kinda stupid telling him.
Now, I always make sure to check the wheel first before using any grinder thats not my own. Plus ,I got kind of "grinder shy" for about 6 months before I really felt comfortable using any hand held grinder at all. Even till this day, its still always kinda in the back of my mind.