When they first met, Spider-Man was able to defeat the Sandman with a vacuum cleaner. However, he's advanced beyond that since then, and Flint Marko is now an incredibly powerful villain able to create duplicates of himself and become a giant sand monster. Not exactly an arch enemy of Spidey's, Sandman has actually fought on the side of the angels at various points in his career, but has never been able to put his villainous traits behind him for too long. He's not that much of a problem for Spider-Man at the end of the day though, and despite what Spider-Man 3 said, definitely didn't kill Uncle Ben.
