I fail at getting the 'What a long, Strange Trip it's been' achievement.
I'm generally about 1 achievement from most of the holidays away from getting it and each year I think 'Right, I'll do it this time' and then each year the holiday event goes past and I've still not got around to bunny ears on my troll char, or doing the fire juggling or something like that.
My main spec is warrior tank. In this field, I feel I am better than average. I time cooldowns, pool/burn rage, intervene, spell reflect, etc. etc. pretty effectively. I run numbers on upgrades and monsters to decide what to use. I levelled almost exclusively in tank, quest in tank spec, and have completed almost every quest in the game, and a pretty sizable number of achievements, again, in tank spec. I have run out of VP upgrades for main spec until 5.3 lowers the bar. In tank spec, I got exalted in 60+ factions, and have gotten most of the blacksmithing recipes too, almost always in tank spec. I hunt rare elites, for sport, in tank spec.
My offspec, Arms, is passable at best. I'm probably at best average, even amongst other casual Arms players. I just don't put in the time or effort to gear, optimize, run numbers on haste vs crit (for example), or work on the rotation.
My highest level alt, a level 90 warlock, is gathering dust in the Halfhill farm, chaining Imperial Silk and DE-ing stuff I send him from my main. He might have 500 quests, but it's probably lower, has two exalted factions (Hozen and Tillers) and his gear is a mix of BoA's and quest blues. My other alts never made it to 40 before becoming bank alts.
My guild has lots of players who have multiple characters and/or specs and they're good at all of them. I know I'm crippling myself by not doing that, and yet, here we are.