It seems that there is no way for a colleague and I to "share" a contact in both of our address books if we both have two-way sync enabled. 

Let's make up a contact, say "Gary" that both I and my colleague interact with and we both want Gary in our Google (gmail) address books. Both my colleague and I have two-way contact sync enabled in Pipedrive. 

I already have Gary syncing between my address book and Pipdrive, and I'm listed as the owner for Gary's record in Pipedrive. 

If my colleague adds Gary to her Google address book, now there are two copies of Gary in Pipedrive - one owned by her and one owned by me. 

This wreaks havoc on our marketing automation system and causes data integrity problems. Plus my colleague can't see my notes or calls with Gary. So we merge the two Garys, like good stewards of data do, and since I talk to Gary more than my colleague, we set me as the owner of the merged record. 

But now Gary disappears from my colleague's address book! She can't email him from gMail and can't invite him to meetings from Google Calendar. When he calls her cell phone, his name no longer pops up. 

So my colleague adds Gary back into her address book and the whole thing starts over again. 

I think there's a key feature missing to contact sync:

On the contact sync tab, there should be an additional option:

 🔘Sync Contacts owned by me
 🔘Sync ALL contacts in database
 🔘Sync contacts that match the following conditions...

Of course, if anyone else has a fix that doesn't require development on Pipedrive's part, please let me know. The battle of the duplicate contacts in Pipedrive and missing contacts in Google must end!!