One of my beefs with Gmail, a service I otherwise like, is its propensity to create duplicate contact entries for the same person without any action on my part.
I'm not sure if this is part of its internal workings for identifying contacts, an issue synchronizing with iPhones and Exchange, or something else, but it's annoying. On more than one occasion I've had to recombine my own entry back down into one contact, and I've had to do the same with my wife's entry, my parents' entries, and others.
Of course, there are legitimate occasions when Gmail might have multiple entries for the same person, such as when a friend whose personal e-mail address you use then e-mails you from her work address.
Google now offers to treat the symptom, if not the disease. There's a new "Merge these 2 contacts..." link that appears when you select multiple contacts. Clicking on it presents a unified entry that you can save, modify, or cancel as you see fit.
(Via the unofficial Google Operating System Blog.)