I flew into Frankfurt at the start of the World Cup last summer, I'm sure they were seeing higher than average traffic but I couldn't tell by the amount of time it took me to pass through customs and pick up my bag. It was an INCREDIBLY fast and painless experience. The wait for my bag was probably somewhere between 10 and 15 minutes, there was no line at passport control, it was just a stamp and on my way through the door.

They may have been staffed at higher levels during the World Cup, but from the previous posters it sounds like my experience is the norm.