I have 4 level 80 characters in World of Warcraft, and I deliberately played them in a way to experience the maximum amount of content, e.g. making the 4th one Alliance to play through Alliance-only quests. While I don't have the achievements to prove it (achievements are character-specific, not account-specific), I'm pretty certain I did 99+% of the quests in World of Warcraft. So for my 5th character to level I experimented with alternative leveling methods, which would not be based on questing.
As you might remember, I leveled my druid to 60 using the Recruit-A-Friend feature, and dual-boxing. That still involved some questing, but significantly less, due to triple xp. But I can't really recommend that method, as it is relatively expensive and complicated to set up, and is limited to leveling to 60. From level 60 onwards, and now up to level 75, I used another way of leveling, nearly quest-free: The Dungeon Finder. Profiting from the eternal tank & healer shortage, I dual-spec'd restoration and balance, as these two specs use pretty much the same gear, and usually went dungeoneering as healer. I also tried doing dungeons as moonkin, but that was only viable in parallel with grinding library guardians to get the schematic for Jeeves, because waiting times for dps are far longer in the dungeon finder.
One of several reasons I wanted another high-level character for was tradeskills. My druid has enchanting and engineering, both of which I didn't have to the highest level on other characters. So making level 75 is a milestone, because it will allow me to still max these out in Cataclysm, 75 being the minimum level for reaching the Cataclysm skill cap. Engineering is more for fun than for being useful, especially since there is very little you can do for other characters, but having an enchanter able to make scrolls is obviously good for my other level 80s as well.
The only quests I did from level 60 to 75 were a handful of easily accessible dungeon quests. The biggest disadvantage of that method is that one is missing out on all the lore, but as I already played through all that lore with other characters, that wasn't really a problem for me. Leveling speed through dungeoneering was at least as fast as through questing, if not faster, as long as I used the rest xp bonus, which applies to dungeon mob kills, but not quest xp. I missed out on all quest items, but that only emphasized the fact that quest rewards for regular solo quests in World of Warcraft are generally useless and far inferior to dungeon loot. In Outlands I got some reputation from running dungeons, but not enough to net me any useful reputation rewards. In Northrend I didn't even get to friendly with any faction through dungeoneering, and ended up spending a few justice points for commendation badges to be able to get to friendly for the tabard which will allow me to gather more reputation in higher level dungeons and heroics. But that isn't strictly necessary, the reputation rewards are far worse than what you can buy for justice points, and the head / shoulder enchants are bind to account nowadays, so I can get them via other characters.
So while waiting for Cataclysm I'll probably still level that druid to 80 with the same dungeoneering method. That is not something I would do with a first or second character playing through an expansion, as I actually like playing through the quests and lore. But playing through the same quests repeatedly is tedious, so for a 5th character the Dungeon Finder provides a good alternative leveling method.