The problem I have had more with "free" on Craigslist is that I get a lot of super-flakey people who reply immediately and then don't show up to take the item after a bunch of coordination effort. I've stopped listing items for free on Craigslist, and I either (1) list it for a more-than-fair but nonzero price, or (2) put it out on the street with a sign that says "free' (only for items that will obviously disappear quickly). Adding the price on Craigslist seems to weed out the worst flakiness-offenders.