For those having Facebook Sync issues.
From another forum..this helped sync missing contacts.
With sync option to "Sync with existing contacts", go into the facebook application and select Friends. From there pick whatever friend you want to sync and press on the picture, NOT his/her name, and then press the contact icon. Hit the menu key and select Edit Contact, then hit the menu key again and select Join. Then from there, it should give you a suggested contact or your entire contact list to choose from. Hit Done.
note: This method is a little picky, and sometimes a friend's facebook name replaces the actual name you saved for him/her in your contact list. I'm picky about how I name my contacts in my phone so this gets very annoying. However, if the facebook name and contact name is almost the same, it should keep the original contact name intact.
Hope this helps!