The upside: Carfax report included. Useful to know what your car's history is... especially if you're selling it as a car with a clean history.
The rest:
I love the site for buying and for advice, but as a private seller, it was a waste of money. I listed my 2006 Accord with a competitive price (mid 4 figures), and yet in 1 month of listing I got exactly 1 message, and the prospective buyer never responded. All the people who were interested in the car, and ultimately its buyer, came from Craigslist.
The dumbest and most offensive thing is that the site - which is all about paying a fair sum to list your ad - doesn't support LINE FEEDS. (That is the Enter/Return key.) Yup that's right, you pay good money to have your detailed ad turned into a jumble that makes you look disorganized and crude.
Speaking of disorganized, I actually called them to cancel my ad (which they did, because it's been just a few hours since I posted it) (of course there's no way to cancel from the site, you have to Call!)... and they did refund my money, but never canceled the ad! :D And because it generated so little traffic, I didn't even notice until I sold my car.