Well this is exactly what happened to me. I had a level 70 Druid and Level 70 Lock - while waiting for wrath had been doing a lot of PvP so I had both with very cool PvP gear on - The lock PvP 70 gear looks sweet (80 not so much).

Anyway with everyone running their 70s in Outland, I thought I would try the death knight - ended up doing an all nighter - Had to fly out for a meeting the day after the release. Anyway I hit 60 with the DK. When I got back I wanted to see how the quests would be in outland - blew through it. By the time I hit 68 and was popping to outland, my guild members were at 72 - 74. I caught them around 77 and just out of respect for the one guild member, waited on 1 bubble to go 80 after him.

So now my main is a DK, I have my lock to 71 and my druid is almost - I drop back and play them a bit, but now at 80 I am constantly looking for heroics.

The druid was my first long drag to 70, learning about alot of things. My Lock was next and I leveled him quite fast since I was familiar with the quests. I have been on wow for just over a year now, so I never had a long long time dedicated to a toon. I am torn I would like to level my druid and lock, but it's hard not to rep grind and run heroics for emblems.