Yeah, I don't know how useful that feature is. What do you think, Neil?
In order to work, there does have to be some kind of written content in the article being posted, and in the case of this thread, there really isn't any. Also, on the admin pages, there has to be a vocabulary of terms in place for each category for the article being posted to be compared to. If categories don't have any terms listed then, no, auto categorization can't work. I suggest reviewing the vocabulary for each category to see if terms are present and if there are more/new terms that can be added.
I think the auto-categorization often does work, but it shouldn't be any inconvenience to users even if it doesn't, as they still would need to manually select a category whether auto categorization doesn't work or if it were turned off (which is why the feature can't be turned off).