I think the bigger obstacles tend to be a sense that player/PC focused "story" is a "sidequest" that should be secondary to the GM's "main plot", which is often set up to be independent of any player/PC hooks. (This is the converse of [MENTION=6688937]Ratskinner[/MENTION]'s point about sandboxes.)
Yep. Having your personal story feel like a sidequest that doesn't have any impact on the "main plot" feels demotivating for a player, especially if you carefully weave a lot of meaningful hooks into your backstory. I guess this is why a lot of posters here are skeptical about APs: Because they need careful planning from the GM beforehand in order to incorporate PC stories in a meaningful, organic way. In addition to the absolute necessity to know both setting and complete AP from the inside out so you don't kill your story before it even started.
However, it can be done when you communicate with your PCs beforehand and invest a bit of time. For my current campaign (WotBS, as I've already mentioned), I asked my players on which characters they'd want to play and offered them some story NPC for whom they could write up connections. After they chose their origins, I read a *lot* about these two backgrounds, their people, their history etc and thought about how I could weave these specific characters into the story so it would be about *them*. It took a lot of work and a bit of creative freedom, but I'm more than happy with the outcome. My players often say they don't know which stuff came from my pen and what originated from the "original AP" and I guess this is a great compliment for any GM
