Slate says that Sarah Palin's biography for young adults has been shelved indefinitely by Christian publisher Zondervan. Whatever the reason, it's certainly not because the bio paints a negative picture of Palin:

In Washburn's telling, Palin's sore subjects are either not mentioned by name or avoided completely. Katie Couric is called only a "well-known journalist" who "came up with a broadcast that emphasized one viewpoint, and it wasn't a good one." Vanity Fair, which published a critical post-mortem on the McCain campaign, is called a "widely read gossip magazine." Palin's 2002 loss in the race for Alaska lieutenant governor is chalked up to the fact that "during this run for office, her passion was surprisingly thin"—in other words, she never wanted to win that stupid election anyway. Bristol's unexpected pregnancy is not mentioned at all; a Zondervan acquisitions editor told the AP that,"We tried to stay away from the super-heavy stuff."

If I had to guess—and this is just wild speculation—I'd say that Palin's people could be working on their own Going Rogue...for Kids! autobiography, in which case Zondervan, which is owned by Palin's publisher HarperCollins, would pull the plug on the biography to avoid cannibalizing their own bestselling author's sales.