Sure its cheating, but it isn't new. Several of Ruth's bats were corked, as were a few other big names. There's some argument as to how effective it is.
One of the funniest episode of this involved Graig Nettles back in 1974. In a game late in the season he hit a home run against the Tigers. The next time up, he hit a broken-bat single and the bat exploded, with six superballs bouncing out as the Tiger catcher tried to scoop them up.