I have been back on this toon recently, only spamming heals in 5 mans to level and I have been having a ball! Leveling time for 60-70 was on par or close to the time it took to do it through questing on my last two toons (rogue and pally) but upon hitting the WOTLK dungeons it has slowed down signifiantly.
Questing gave me about a level every 1-3 hours for my pally / rogue in 70-80 but I am only 1/2 way through 70 on my shammy and have done about 10 dungeons over 3h for this level. I did 32 dungeons to level 60-69 (Average of 3.5 per level), I have now done 9 in WOTLK for only 1.5 levels.
I realise that a 20% exp "buff" is coming for WOTLK areas however leveling through LFD will be much slower than questing. I think WOTLK dungeons are far below par for exp/per hour, compared to BC.