If you are running a Drupal multi-site installation, and the sequence tables are shared, then here's an admonition: take real care of the changed prefix for each shared database. Cross check on the sequence tables if you ever had to rename the database or just the unshared tables.
For instance,
[dbprefix_dbname]
becomes
[dbprefixnew_dbname]
The first thing you have to do is go check the sequence table and change the values manually on the new sequence table entries corresponding to the database appropriately.
I finally got my copy of Pro Drupal Development yesterday. Drupal has changed lives of many in past several years, and mine isn't different. It was not just the curiosity about what's in the book that made me buy it, but also the opportunity the book provides in filling gaps of what you might have overlooked in hurry.
I've been reading through the book whenever I've had time for past one day. The book looks well structured and simple.