I have a confession to make. I have played WoW since late 2006, and I have yet to get a second toon to max level, in any expansion. I'm not entirely sure what's made this nearly impossible for me -- I've certainly had multiple toons since the very beginning, but never took another one to max after I hit 70 on my night elf druid. Then I never took one to 80. Then 85. And now 90.
I have a few that are getting close, a paladin around level 83 or 84 right now, and a mage that has been steadily climbing over the last couple months and is now level 53. I would love to have a small army of alts. I dream wistfully of a self-sustaining pack of toons, who can farm and craft each other what they need without me ever having to drop 500 gold on a stupid gem ever again. Of course, even if I play madly until the next expansion comes out, I probably won't quite have that setup, but I feel like it's a reasonable long-term goal. Hopefully I'll achieve it within my next seven years of playing WoW, though.