I saw the G4 show Cheat, and they had a quick tip for Super Mario World..
If you go through the goal at the end of each level when the last two digits of the timer matches the digit in the tens place on your star counter, you get extra points (ie: 42 stars means going through when your time looks like x44, where x is any number).
They also said that if you go through carrying an item, that item will become another 1-Up, but the video clearly showed that when Mario carried an item through the 2 goals that they were showing, the item became a Super Mushroom and was stored in the box at the top of the screen.
G4 didn't say this, but the items become something depending on how powered up Mario is, and if he has an item in reserve.. I can't remember exactly how it went, but I do remember that some special items (keys and Baby Yoshies) become 1-Ups when carried through the goal, no matter how powered up Mario is.