I'm a newbie (just started climbing outdoors in July) and with the exception of the guided climbs I've done at Smith, I've only climbed with cc.comers. Everyone has been great, nice, patient, helpful and I hope to climb lots more with each of them.
As for how to judge a possible partner found on this site... when I was going to climb with someone up Seattle way, I PM'd a cc.comer (a couple, actually) and asked if this guy was safe/okay to climb with. Also, depending on where you live, go to a pub club. Seattle has a bunch of them. That's how I got to meet some of the PDX climbers.