I live in Phoenix, Arizona, so I don't need these most of the time.  But we just went to South Lake Tahoe at the end of February, and knowing how thin-blooded I am, I figured I should get something like these to keep from becoming miserable on vacation.  These work great!  They are thin enough to fit into my regular shoes, yet thick enough that my feet never felt cold.  We went to the top of the Heavenly Ski Run, and my feet stayed toasty.  Yes, I was also wearing hiking boots, but that just meant my feet didn't get wet when I tried to build my very first snowman.  (Yay - one more thing off the bucket list!)

So while I probably won't need to wear these next winter in Phoenix, I have to say that they really helped my snow vacation stay comfortable.