I think the only one of my characters that did ST at the suggested levels was my main priest. All the other alts just leveled right past most of the Azeroth instances and ran through the portal at 58. My lock did do ST once at 70, I ran some guildies through it so they can get their quests done. For the hell of it my hunter went back to get it at 70, it's been sitting in the bank since then.