DraXxuS
From my experience you get more used to getting hit over time. As both a player and ref I've pretty much taken a hit to just about everywhere except my face.
Still there are some tender areas that still gonna sting pretty bad no matter how used you are to it. Most hits I can't even tell where they are at the end of the day unless they are in a tender region.
It's definnitely one of the things you learn to tolerate. In my case, that took about a month to get used to getting shot since I played at a primarily speedball based field. lol. But yeah, getting shot in the kidneys, adams apple, etc all suck a lot. Dunno why, but lately people have been shooting me in the a** while I ref. I lay down on the ground to stay out of lanes so they see me and are like...POW! My gun miss fired? lol. But yeah. You definitely get used to it if you ref.