No slip, rear wheel was perfectly straight as ever, and the chainline was still perfect after i stopped and put it back on, and no it didn't break. I use a 12" wrench w/ track nuts to tighten my rear wheel down. Chainrings perfectly true too. I reset the tension after limping it home with a saggy chain and then went back out, and even then I still came back and had noticeable less chain tension than when I set out.

I'd have to disagree with Mr. Brown. While I know the chain does not literaly stretch like an elastic band, I think it does enlongate over time. When I was riding BMX we had the same issue with chains, you would take them on one ride and then get nearly a halflinks worth of slop. It makes sense to me, I mean there is some room I'm sure for the pins/bushings to settle in seeing as they never experience any sort of load until they are on a bicycle, so it seems to me that a ton of load like a new chain would experience on a fixie would stretch the chain out fast.