I used to crochet so much that I wore a groove into my yarn-holding finger. When it would start hurting (as in cutting really deep), I would slap a band-aid on it and keep crocheting. It's gone away now that I knit more than I crochet!
My friend was determined to knit while she was in labor with her first child, and she would have, too, except they stuck something (monitor of some kind, I think) on her index finger, and she couldn't maneuver the yarn. I have to give her credit, though: She tried!