I'm having the same problems on my PowerMac and MacBook Pro running 10.6.4. It seems to have broken with one of the latest software updates.
When adding to or editing Address Book or iCal very useful predictive autofill suggestions relating to each field would be displayed ( ie, if I typed "Au" in the country field for example, Australia would appear as a suggestion). This very time saving function has ceased to work. Any ideas on how to get it back up and running?
I'm running OSX.6.4 on an mid 2008 Intel Core 2 Duo, 2.8 GHz iMac.