Yep. I've done it a few times. I've done double headers at the same school, and those are fine. But the different venue thing usually just stresses me out. If the drive is tight, I don't always arrive mentally ready to work the game.
My worst case: I was helping the assigner out, and we both knew it would be a stretch to make tip-off of the second game. Of course, the inevitable happened (first games went long, traffic was bad, etc.) and I didn't arrive at the second assignment until just after the second half began. My partner was a ref who was so bad that he was asked not to return the following season.
It was just such a bad experience. And it made no difference knowing that my assigner knew this was a very real possibility, or that if I had not bailed him out my partner would have had to work it alone. All anybody there cared about was that I was very, very late. I could hardly look the coaches or players in the eye.
But at least I got to relive the feeling all over again a week later when the game check arrived in the mail -- for 1/2 a game.