Eschewing heirlooms, in fact, is merely the tip of the iceberg when it comes to self-imposed constraints on leveling. Noor the Pacifist was one of the first players to gain widespread attention for leveling up in a quirky fashion; he managed it entirely without personally killing creatures or other players. Then there's neutral pandaren Doubleagent, who recently reached level 80 without ever having left the pandaren starting island (and he's still going). There are players who've leveled without training any talents. And incredibly, there's a whole host of players who've embarked upon what's known as the Ironman Challenge, leveling to 90 with no gear, no talents, no grouping or professions and the reality of considering any death a "perma-death." Ouch.
If you too enjoy setting self-imposed restrictions to spice up your leveling experience, what's your poison? What makes the added twist so enjoyable for you?