The first time I attempted to use Mozilla Thunderbird's import function to bring my Gmail contacts into the client e-mail application, I was seriously disappointed with the results. Most of the contact information was squished into a single nondescript field for each record. The few fields that did make the conversion were incomplete. The entire process was pretty worthless, overall.
Then I found the free Zindus add-on for Thunderbird. The program brings a subset of contact fields from Google and Zimbra into Mozilla's free e-mail program. For Google, the fields imported include the contact's name, primary and secondary e-mail addresses, phone numbers, IM names, company, title, and notes. (I didn't test the program with Zimbra.)
After you download and install Zindus, a "Zindus" option is added to Thunderbird's Tools menu. Clicking it opens the Zindus Configuration Settings dialog box where you're presented with a handful of contact-sync options, including a Sync Now button.
Start by clicking Add to open the New Account dialog box. Choose either Google or Zimbra, enter your address and password, choose the account you want to sync contacts with and whether to include Google suggested contacts, and click OK to add the account. Back in the Zindus configuration window, select the account, and click Sync Now to begin the process.
When the import completes, a new address book appears in Thunderbird with the default name of the account from which the contacts were imported. You'll also find the Zindus icon at the bottom of the main Thunderbird mail and address-book windows. Click it to sync your Google contacts with Thunderbird.
The import process isn't perfect; expect a good amount of cleanup as information in different fields gets merged here and there. But what I really need are the e-mail addresses, and these come through the import process fairly well.
As soon as I begin to enter an address in the To: field of a new Thunderbird message, I'm able to select the addresses I'm sending to from a drop-down menu that lists all the addresses beginning with those letters. That's all I really need. Sure, it would be nice to generate mailing labels from Thunderbird contacts, but there are better ways to create such labels.
Maybe someday we'll be able to enter a contact's information once and have it available in all our applications that require it. Until that day arrives (I'm not holding my breath), free services such as Zindus fill the gap nicely, if not particularly precisely.