Slayer in 2007Last year marked the inauguration of the Rockstar Mayhem Festival tour, a summer package from the creators of Warped Tour that featured heavier acts. There were some pretty surprising bands on the bill: besides Miami's Black Tide, performers included Mastodon, Underoath, and Of course, if you're a Slipknot fan, that band was the ultimate draw as it celebrated its high-profile return.Besides some really gross on-and-off rain on that boiling July day, the place was packed -- so