Ok, if I'm following this right.... I've manually set up contacts in my captivate but do not have all their email address. I've spruced up my Gmail account Address Book that includes all the email addresses. If I sync these two (my phone w/ Gmail) I will see the duplicates, but one set will not contain the email addresses, so I will have to manually delete each one, right?
Umm...not quite, unfortunately.
Gmail is one database.
Your phone contacts (the ones you entered as "phone" in that are NOT in gmail) are in another database.
What Android does is link the two databases together via something common, most likely by name...but each database does NOT *sync* with the other; they remain separate databases...So if you DELETE the phone contact, it goes poof! - no more phone numbers. If you delete the GMAIL contact, it goes poof! - no more emails.
If you want ALL the data resident in ONE database (phone numbers, email, addresses, etc.) -- your best bet is to enter them into GMAIL online. Then instead of deleting the phone contact, you can actually just hide or "not show" phone contacts on your phone, so that all the contacts you "see" on your phone come from gmail.
I had to do this myself. Not fun, but not that bad if you're doing it on the computer. On the phone, it's slow going.
EDIT: One thing you might consider is to EXPORT your PHONE list into VCF and then IMPORT into GMAIL. Then in GMAIL, you can "merge" records. But I can't exactly remember if I did this in Google Voice or GMAIL...but in one of those two Google clouds, I merged the duplicate records into one, as needed.