Hand-me-downs

One of the big new things they introduced in Wrath was Heirlooms. Basically it's a piece of gear your alt will never have to replace while levelling from 1-80. The item is equippable at any level (given you meet the armor/weapon proficiency and all that) and scales as you level up, with the stats being slightly better than the best blue item you can equip at that level.

But the main reason people use heirlooms isn't because of the convenience, it's the fact that they give experience boosts. Heirlooms shoulders and chests EACH give a 10% xp boost which stack. So if you were levelling an alt who had heirloom shoulders and chests, you could level 20% faster than a non-geared alt.

With the launch of cata came two new types of heirlooms - capes and hats. I don't believe anyone out there has obtained the hats yet since it requires guild level 20 (guild xp gains are capped per week), but the capes are attainable at guild level 10. At 1200g apiece it's a bit pricey, but they give an additional 5% xp boost! The hats, when they are actually available, will be adding another 5% xp boost.

In addition to just armor, there are a whole slew of weapons (melee, caster, ranged) and even trinkets (physical/magical). Given that you don't even get a glimpse of trinkets until level 45-50 or so, the heirloom trinkets are very nice to have, if not for the stats themselvs, then for the sake of not having empty item slots.

The Pros:
Obviously, the vastly increased pace of levelling. While the combined bonus of the chest, shoulder, and cape add up to 25%, in reality the levelling speed is much greater. Obviously it's not something I have actually measured since levelling speed depends so much on your play style anyways, but you can definitely FEEL that it's way faster than 25%, especially in the early stages of the game.

Why? Think about this - a freshly created level 1 character starts out with what? A few basic pieces of armor and a weapon.

Now in comparison, what does your uber-pimped out alt have? Chest armor, shoulder armor (the lowest level non-heirloom shoulders are equippable at level 15), a weapon (2 if you can dual wield), ranged weapon, cape, and 2 trinkets.

So while Mr. Noobsauce over there is taking 10 seconds to kill that level 3 boar, you're mowing through, one-shotting boars left and right. While Noobsauce has to carefully fight one-on-on, you're pulling 2 or 3 at a time. When Noobsauce accidentally falls off that rock and dies, you easily survive the fall with your high armor and hp. When that tough quest mob kills Noobsauce, you're yawning as you take him down with two clicks of the mouse.

The Cons:
I know, I know, what can possibly be bad about heirlooms? Well, in my opinion it sort of ruins the levelling experience. Don't get me wrong, if your goal is to powerlevel to 85 ASAP and start raiding because you've seen and done everything already, by all means mow through the content. But I play my alts purely for fun. All of my energy and focus for raiding is spent on my main, and when I log onto my alts, I just want to do some fun little quests, maybe actually see the storyline unfold in a particular zone I've never been in, level some new professions for fun, etc etc. And of course, squealing with excitement at gear upgrades. But when you're decked out in heirlooms, there's no such thing as a gear upgrade. You can't really fully experience a zone because you level through content too quickly. There's no real challenge in fighting anything - elite mobs, group quests, whatever. You know you'll just two-shot it.

Of course as you get into higher levels, the discrepancies between a non-heirloom and an heirloom char become lessened. At level 60 you will probably have only a slight edge compared to Mr. Noobsauce, who has by now acquired almost full blues from all his dungeoning endeavors. You will still have that permanent 25% boost, but you're probably not mowing through mobs like you did back in eversong woods.

I use heirlooms because I like to have my characters wearing the best stuff they can possibly get. The levelling speed is a bit too quick, but I still try to take my time to enjoy the questlines in new zones and once in a while actually reading the quest text. I also put time into my professions, even secondary ones like cooking and fishing which most people simply ignore on their alts. Once you get to 85 there really isn't much to do besides raiding end-game content. While that's very fun at times, it's nice to stop and smell the peacebloom once in a while too.