If you sync your Google contacts between multiple devices or pull from multiple email accounts, you’ve probably got quite a few duplicate entries. Now your Google and Gmail contacts let you kill those dupes en masse with a single button.
Hit up your contacts from Gmail, or head to google.com/contacts, and hit the “Find duplicates” button in the lower-right area. You’ll be provided with the list of contacts with at least 2 entries each, which you can view in expanded form, and then either merge together or kill off. Not that this is some new-fangled tool or an advanced feature, but I know at least a few Google users’ primary annoyances with contacts can be salved, if not cured, with this little button.
One button to merge all duplicate contacts [Official Gmail Blog]