In September 2004 I travelled from Toronto to Buffalo by train. After entering American soil the train stopped, and law enforcment officers with dogs embarked the train, in order to do their job. The procedure lasted approximately 70 minutes, although there weren't much passengers aboard.
Maybe I contributed to the delay, because they had to bring me a I94-W form because of my Austrian citizenship.
Next time I won't take the train, it's too uncomfortable for passengers.