Last time this was discussed, people posted excerpts from Craigslist's terms, in which the user grants Craigslist the right to (i) Use their post, (ii) defend against others copying it.
So, I haven't verified it, but the idea seems to be the user owns their post, and could post it elsewhere if they wanted - but Craigslist has the right to stop other sites copying posts direct from Craigslist.
There was a recent case where the judge ruled that a company that didn't own a copyright, but was assigned a license in order to sue infringers on the owners behalf, didn't in fact have standing to sue.
So, I haven't verified it, but the idea seems to be the user owns their post, and could post it elsewhere if they wanted - but Craigslist has the right to stop other sites copying posts direct from Craigslist.