This afternoon, a overconfident rogue on my server was claiming he had soloed MC up to Domo at level seventy in the trade channel. Anyone who laughed at him was told "Yeah, why don't you come outside and duel me and then say that?" Then he threatened to report everyone. Good times, good times.
Although this rogue was clearly full of hot air, other people are now going back and seeing what they can do with the level 60 content. A healer/tank combo two-manned a 45-minute Stratholme run a few days ago, and a druid and priest killed Bloodlord Mandokir in ZG last week, although it did take them over half an hour and they exploited. Some theorycrafters are wondering how many level 70s you would need to do MC all the way through. The only concrete number posted was fourteen, but that included some lower-60s players. Since so many of the fights in there are curse-dependent, you'd need some pretty strict class composition.
I've thought of going back and seeing how much of UBRS or Strat I could solo, but since I'm a rogue and can't heal myself, I probably wouldn't get very far. Have you fought any old content? How much do you think you could get done with a 5-man group?