Agreed, I've come to view callbacks as a tool to enforce application-level data integrity and relationships, not a place that higher level business logic should live. The line is often fuzzy, but I think the question you alluded to, "should this happen with every conceivable create/save/etc.?" is a good general guideline.
One thing to keep in mind when moving logic out of callbacks is that you'll no longer get the implicit transaction that ActiveRecord wraps around the whole callback cycle, so you have to be a bit more hands-on with managing transactions.
And even if it happens for every create, the fact that the author had to do so much more work just to make something like this work is a sign that Model callbacks may not be the best solution.
One thing to keep in mind when moving logic out of callbacks is that you'll no longer get the implicit transaction that ActiveRecord wraps around the whole callback cycle, so you have to be a bit more hands-on with managing transactions.