Back when Swissair still existed and had a partnership with Delta (including a DL flight attendant on SR flights to the US) I was flying ZRH-BOS.

The problems started when a passenger's passport looked off and the gate checkers picked up on it. They tried to check with US INS (as it was then) to find out if the passport was legitimate or not and were unable to verify it, so the passenger was removed. For whatever reason they also weren't sure if that passenger had checked any bags, so the entire luggage compartment was unloaded onto the ramp and we were escorted down there in small groups to identify our bags for re-loading. This took a while; after all these delays we were told that the crew was no longer legal to operate to BOS. A reserve crew was called in, and eventually arrived; I think we left about 3 hours late.

By the time we got to New England, BOS was being hammered with thunderstorms and we circled off Cape Ann for a while (the weather was jealous of the attention given to the passenger/baggage/crew delays). I think the total time was >12 hours gate to gate. I was very glad I'd packed extra books.