I've been doing a priest+4lock group and just hit 19. 1day4hours /played right now, so a bit more than an hour per level. I did all the quests in the UD starter areas and all the sub-18 ones in Silverpine (stopped at berin's peril).

On the other hand, I just ran Ragefire Chasm at 18 in an hour, so I was fairly happy for mostly nekkid longevity of these guys.