I once made arrangements with a fellow from CL via E-mails to take a look at a bike while he was out of town [lived in a very low-crime area and said he would leave it on the porch and I could just leave a check in mail box if I'd like to purchase it (was a ~$35 beater Gary Fisher MTB)]. So said seller leaves me address and Phone #, tells me to call him if any issues. Sounds goods to me so far.

Decided to have a friend ride with me as the house on Google earth was a good distance from others, even though he said he would not be home. Eventually found the place, no bike. Called the man twice and left a message before I left only for him to call back and accuse me of: trespassing on his property and hacking into his e-mail address to find his contact information?!?! He said he had no idea who I was so i referred him to the e-mail conversations where he addressed me by name (which is when I was accused of hacking).

Long story short. Be very careful with CL. Always take someone with you to a meet. Speak to them on the phone beforehand to get a grasp of character.
That being said, if proper precautions are taken, CL is a great, free resource