Just about every day. They recommend you put the arm under the fender. Another poster here did the opposite and the driver had to pull over to allow him to fix it. I mounted my front fender a tad higher to allow for the clearance. Plus, both SKS and freddies bend fairly well.
Oh and when you first put it on the bus do not freak out that the bike is wobbling as the bus hits bumps. It's supposed to do that to a degree. I've had my bike on the bus 100s of times with no issues. Now that I have cursed myself I am going to find some wood to knock on.