I'm not a big fan of the People Hub view in Outlook 2013's contacts. It's too cluttered, it's confusing. While you can edit contacts in the contact cards, it supports only the main contact fields. If you want to edit the contact photo and add (or open) attachments, you need to open the full contact.
I don't recommend using this key with the new autocomplete dialog that lists Recent contacts and Other Suggestions. If you do, you won't see Recent contacts in the autocomplete list.
Accusations that Outlook is too complicated are right on target when it comes to contacts. Many new users are confused by Contacts and Address Books. Outlook 2013 gives us more confusion with contacts and contact cards, and search results that include the auto-complete list.
Yes, you heard right. Search People (formerly Find a Contact) results include addresses from the auto-complete list.
Most people probably wouldn't notice, but it's clear from my Search People results because of the entries for messages associated with a moderated mailing list I own.
Following the April 2016 updates, you can remove the autocomplete cache from People Search results in Outlook 2013 and 2016. Instructions are below.
While it should be easy to identify auto-completes because they usually don't have friendly display names, they clutter the search results and can't be deleted from the results window; you need to remove it from the auto-complete list or set the DoNotIncludeNickNameCacheInSearch registry value.
To edit the registry, press Windows key + R to open the Run command. Type regedit in the Open textbox and click OK. Browse to the correct registry key for your version of Outlook and add a new DWORD called DoNotIncludeNickNameCacheInSearch. Modify the value, changing it to 1. Note: if the keys in the path don't exist, create them.
You'll need to restart Outlook after setting the registry value.
Do It For Me
If you don't want to edit the registry yourself, you can run a ready-to-use reg key to set the value. Dowbload the appropriate file, change the extension to .reg if necessary, then double click to run it and follow the prompts. Then restart Outlook.
To remove non-existent contacts from Search People, you can delete one address at a time by starting a new message and typing the first letters of the address, then selecting the address and deleting it, either with the Delete key or by clicking the x beside the address. Close the message form when finished. You can clear all names from the list in File, Options, Mail. Look for the Send Messages section halfway down and click the Empty Auto-complete List button.
Search Tip: Dock the Peek
Dock the People peek and search in it instead of using the Search people command. While it also includes entries on the auto-complete list, the window can be re-sized to display more entries and the search results will stick around until you clear the search.
To dock the peek, hover over it and click the dock button in the upper right corner. You can also right-click on the word People and choose Dock the Peek
The docked peek keeps the search results in view until you clear the search or un-dock the peek (click the X in the upper right corner of the people window to close it.)