My PowerBook (or iBook) will not go to sleep when Speakable Items is enabled from the Speech control panel. Is this normal?

Yes, this is normal. When the sound input driver is in use (this driver is activated by the Speakable Items selection in the Speech control panel) a PowerBook or iBook will not go to sleep on its own. However, it will still go to sleep manually when you select Sleep from the Special menu or when you close the lid.

If you would like your PowerBook or iBook to go to sleep after the time specified in the Energy Saver control panel, you must turn Speakable Items off.

Also, third-party applications may enable speech recognition without notifying you. If such an application is open, the computer will not sleep on its own.