http://us.blizzard.com/support/artic...rticleId=20588

Some of the cooler things:

What in-game benefits do we get while the accounts we play are linked?

1. Characters on both accounts can summon each other once per hour.
2. While adventuring with your linked friend/family member, you will each gain triple experience and honor.
3. For every two levels the new player earns, the new player can grant one free level-up to a lower-level character played by the veteran player.

How long will I be linked to my recruit?

The link between the accounts will last for 90 days from the date that your recruit creates an account. Remember that for the link to work properly, your recruit must create a new World of Warcraft account using the 10-day trial key in your invitation email.

Is quest experience tripled too?

Yes, but only if the quest was not trivial (gray difficulty) for either character.

What if I'm partied with multiple recruits who I'm "linked" to? Do I get quadruple, sextuple experience?

No, you can only ever gain a maximum of triple experience regardless of how many linked recruits you are partied with.

How can I earn the exclusive in-game mount?

For each person you refer who upgrades to a retail version of World of Warcraft and purchases two months of game time, you will be able to give a character on the account you sent the invitation from an exclusive in-game zhevra mount. This unique mount can be claimed through the website, is only available to Recruit-A-Friend participants, and can only be applied to a single character.

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In theory if I understand the free level up correctly, a new boxer could create one account and invite 4 others which in turn could cause 4 other toons to reach 35 without ever being played.