Here's an easy, low cost way to do it:http://danceswithwool.wordpress.com/2008/11/28/knitting-tips-non-slip-sock-bottoms/
Cool idea! I make slippers for my 82-year-old mother. I'll have to keep that in mind the next time I make a pair for her!
I've also read that puff paint works well too, but I've never tried it.
I like this idea a lot. I have slippery slippers! (maybe that's why they named them "slippers" in the first place?...LOL, never thought of that before, hehe