Power leveling has been around for as long as MMORPGs. Usually, players power level by convincing a maxed out character to grind high level creatures while they wait nearby, accumulating XP at a higher rate than usual. While power leveling is an effective way to level, it involves inconveniencing a friend, setting up a second account, or paying another player fees between 10 and 20 gold per level. Power leveling inherently skips players over the early levels, a time when they are expected to learn how to play their new character effectively.
Another option for accelerating the monotonous leveling phase of a toon is grinding with blessings. Doing so speeds up the leveling process while also allowing players to learn the mechanics of their new class. The blessings, [Saintly Blessing (Small)] and [Saintly Blessing (Big)], are sold by the rune merchant for 10 runes per stack of 10 small blessings and 25 runes per stack of 5 large blessings. These blessings stack as well (thanks to MuffinTop on AF for the tip) and running both simultaneously costs 6 runes per hour. Note that these blessings only affect kill-reward XP, not quest-reward XP.
I am definitely against the free-to-play model for armor and weapons, but when it comes to leveling, the alternative of not using XP potions is readily available and yields the same results. I purchased the $50 rune pack for $25 during the last half off sale. Also, Best Buy regularly discounts iTunes gift cards to 80% of their face value, for example, $20 for a $25 gift card. Time it right and buying blessings is not very expensive: I picked up 320 runes for $20 (20% off $25), or 6.25 cents per rune. With those discounts, one hour of grinding with both blessings activated comes out to a whopping 37.5 cents. Not too bad, is it?
Over the last double XP weekend, I acquired 2000-3000 XP in my mid-30s (level) for each elite humanoid that I killed in the northern desert. I went from level 35 to 40 in two hours, possibly less, of casual playing. Totally worth it if you ask me!
I’d recommend playing through the game at normal pace with your first level 60. It is a rewarding experience that should not be missed. After that, all of these techniques are fair game, assuming that they don’t violate the Gameloft’s T&C’s of course. 
Also mentioned in an entry on my personal O&C blog, Mage.Awesome: Level 41.