While trying to test this hint earlier today, I was somewhat dismayed to find that speech recognition appeared to be broken on my G5 -- I could enable speech recognition, but the Speech Commands window (which you can display by clicking the small triangle at the bottom of the floating Speech bubble) was completely blank, and the computer wouldn't respond to any spoken commands. Under some deadline pressure, I switched to the PowerBook, where speech was working fine, to test the hint.
After getting today's hints up, though, I wanted to solve this problem -- not because I use speech recognition a lot, but because I don't like it when parts of my machine don't seem to be working correctly. My first stop was Apple's Knowledge Base, which has become a fairly good troubleshooting resource. A search on blank speech commands let me to an article called Speech Recognition - computer does not respond to spoken commands. Though a number of possible causes are listed, it was the last one that caught my eye:
5. Mac OS X 10.4 or later only: Check Address Book entries.And that's exactly what was causing my problem. My Cingular phone, when synced with my Address Book, had created a number of "company" entries for things like billing balance, customer service, etc. All of these had blank company fields. As soon as I unchecked these null items in the Address Book configuration area, my speakable items instantly reappeared. Since this was a bit tricky to diagnose, I thought it worth a reference here...
In Speech Recognition preferences, click the Commands tab. Select Address Book in the command set and click Configure. Any contacts named "(null)" could lead to this issue--these are contacts you have designated as a Company but did not enter a name for. To fix this, open Address Book and ensure that contacts designated as a Company have a Company name. If you do not need to make this contact speakable, you can deselect the box next to this contact in the Address Book Configuration pane of Speech Recognition preferences.

