If you listen to me (or anyone else around here, it seems), the major consensus seems to be to head to Outlands right at 58, period. The leveling is faster, the quests are more interesting, and the money is plentiful, as are the drops. But cyanrose over on WoW LJ makes an amazing case for exactly the opposite: staying in old Azeroth from levels 58-60.
She's been rolling around Hearthglen picking up items and XP, and from the way she tells it, things are almost as good there as they are in Outland. A dropped Orb of Deception (which was sold for a whopping 700g) didn't hurt, and there's lots of Rich Thorium around as well. Since old Azeroth is so empty, she hasn't had any problems with PvP, and apparently there's some good AoE grinding to do around there as well.
Great example of going against convention and finding your own way to play through the game. Outlands is there if you want it at 58 -- you can replace your gear in just a few quests, and get started on the new reputation grinds early. But don't let the popular opinion stop you from exploring the old world if you want -- there's lots of loot and fun to be had there, too.