On my wizard, earlier today I went from like 40 to 51 (from 51 to 52 the exp required per level jumps by about a million) doing quick Zultan Kulle runs in Nightmare. I had only cleared up to the start of Act 3 at that time. Since I was 51, I bought a set of good gear, loaded up Act 4 normal, then exited the game and used the public game trick to skip to act 4 NM, killed Diablo and auto unlocked Hell. Ill likely at some point use that same trick to skip from where I am now (Act 1 Hell) to Zultan Kulle, farm him until 60, then skip to Act 4 and kill Diablo on Hell and unlock Inferno.
/shrug. Until Blizzard patches those two its fairly easy for you to powerlevel yourself. Those 3 or 4 hour level 60's though, I dont know wtf they are doing. Kulle runs are fast leveling, but its not THAT damn fast.