Hi alpinepower,
Do you happen to have omnigrowl installed as well?
I had the same thing suddenly happen when I removed all my items at startup and started to replace them. I couldn't figure out which one of the startup items was causing it, but by FLUKE launched the prefs of omnigrowl just as it started up (command - comma).
In there you'll find a check box that says "Launch Address Book" - uncheck it.
Hope this helps!!
-sb-