I have just upgraded to Ubuntu 12.10 myself just to find that Startup Disk Creator is broken. It crashes before completing a USB startup disk. Turns out it's a bug and it has already been reported. Fortunately there is a simple workaround until this bug is fixed. Use UNetbootin:
Now you can launch UNetbootin and make your USB startup disk. I hope Canonical manages to fix the crash soon so we won't need to do this.