Looks like some weekend warrior at Amazon is at it again. I tend to pre-order most Pathfinder products as soon as Amazon lists them. I've had the "Advanced Race Guide" ordered since the book appeared.
This morning, Amazon sent me the following:
"Due to a lack of availability, we will not be able to obtain the following item(s) from your order:
Jason Bulmahn "Pathfinder Roleplaying Game: Advanced Race Guide"
We've canceled the item(s) and apologize for the inconvenience."
They did the same thing with another book a few months ago, again on a weekend and Paizo's Sales Department was able to straighten it out. I hope they can convince someone at Amazon to stop being so quick to cancel orders. Hell, I've had items pre-ordered on Amazon sometimes for years.