Ever since I got comfortable with the method, I haven't had any problems with ladders. I only really did on the first "real" project I used 2 circs for (sweater sleeves) and that was a LOT of knitting, so by the end, I had it down.
Do you just tug really tight between the joins? I just finished my first hat on 2 circs (used the Boye's trick with one set of needles Amy posted about -worked great), but I had ladders between the joins. I thought I was tugging tight but maybe not tight enough, and I tend to have too much tension.