If you're anything like me, it can sometimes be difficult to keep a large address book of usually automatically created contacts in order. It's easy to find contacts in my list that have three or four different entries -- one with just an email address, one with a home phone number, and one with a mobile number.
In an attempt to clean everyone's contact lists up -- Google has created a tool that can organize your contact list with a single click. Just go to your Gmail account, click "contacts" and then hit the "Find duplicates" button.
You will then see a list of contacts that Google knows how to merge -- at this point, you can tell Google to ignore any that you want them to leave alone before Google goes ahead and does it's thing.