I use the hardhat/muff/face shield combo all the time.  Also wear leather gloves.  About half the time I wear sunglasses as well.  
I have never owned a pair of chaps, but used a pair once during a summer job that consisted of about a month tree culling.  In that time I had two accidents.  One kickback that resulted in a small cut on my chin (scar to this day which could have been prevented with the face shield) and another where I laid the saw bar on the chaps before it was done running.  Stopped instantly, but messed up the chaps.  Leg was untouched.
Also, a few years ago I was cutting wood for spare cash (bad idea) and a limb fell on me.  Busted some teeth and got a mild concussion, along with some stitches.  Could have been prevented with a hard hat.
Too many close calls for me.  Coincidentally, this morning I ordered some chaps from:
<A target="_blank" HREF=http://www.baileys-online.com>http://www.baileys-online.com</A>
Price: $42
I think that everyone would agree that a pair of legs is worth that.