Okay, I found some more pipe bugs. In 4-1 , 6-1 , 6-4 , 7-2 , and 8-3 are pipes that drop Mario off into thin air to his death.
7-2 , 7-3 , and 7-4 have pipes that let Mario skip to the last segment of the level.
7-4 has a pipe that warps Mario to the end of level 7-3.
8-4 has a pipe that warps Mario to the same pipe.
Finally, 8-5 is really damn hard. Not in a bad way though.