I'm thinking this is a moderately good thing: it has to mean that the book's selling at least a bit better than their buyers expected. On the other hand, if they don't have mine, does that mean people will buy some other book instead? Some will, no doubt.
Update (Monday a.m.):
Amazon sales rank: 1414
Barnes and Noble sales rank: 357
As Jack Nicholson said in Mars Attacks, that ain't bad.