I have loved CL since its inception when it was still listfoundation.org.
I've been a personal friend of Craig for 10+ years (before he started the list! met him at a LISA/Usenix conference way back when). He's a great, really sweet guy.
Have mostly used the Silicon Valley/SF/Bay Area site, and bought and sold dozens of items including computers and cars. Never had ANY problems with anyone.
I've also found apts, subletted my own apt. and found roommates numerous times; gone on dates, found babysitters, etc. It is awesome and totally works.
Common sense is really enough to stay safe -- cash only transactions, and for larger items (cars, etc.) write up an informal sales contract.