Grantable levels, 300% XP boost, and the summoning of linked account friends in a party with you remains the same. And, as WoW Insider recently reported, the Recruit-a-Friend bonuses now extend to level 85.
By far the biggest change is the rewards. Once your friend has purchased game time, you'll get a notice that you're eligible for rewards. The reward is chosen in-game from a browser accessed via the friends list, and you can pick from exclusive battle pets, the new Emerald Hippogryph mount, and every previous recruit-a-friend mount.