I guess it is fair to say that I have been struck with Drupal fever. But I wouldn't go so far as to say I've learned the chords for the Drupal Song. I have moved over the initial hump of learning curve and slowly I'm making my way down the smooth segment towards advanced-beginner. There is a lot of documentation online to get going with Drupal but it is often hit or miss. Quite often it is outdated, mostly due to how fast Drupal moves.
It's not very often I'd say this but these books do a great job introducing core Drupal ideas, far better then any single tutorial I've found online.