I mention this in case anyone out there is thinking of multiboxing but hasn't yet taken the plunge. 5 accounts can be daunting at times
I played a mage/priest or rogue/priest duo all the way through vanilla (1.0) content and raiding. Once TBC hit and all my friends outleveled me (damn work schedule!) I added three more accounts so that I could instance grind while they were raiding.

Two accounts was a lot of fun, being able to clear heroics on my own schedule is pretty great as well