Ahhh!
Probably with the import the default custom fields have been removed.
In a clean install there are: Skype, FB, Twitter, LinkedIn, G+ (plus the... well, whatever... AOL, ICQ and Yahoo! Messenger).
For the record.
Facebook
* Wrap user input in text
<a target="_blank" href="https://www.facebook.com/{INPUT}"><img src="{DEFAULT_IMAGES_URL}/profile/facebook.png" alt="{INPUT}" /></a>
* Input Mask => Regex
~[a-z][0-9a-z.-]{1,31}~i
Twitter
* Wrap user input in text
<a target="_blank" href="https://www.twitter.com/{INPUT}"><img src="{DEFAULT_IMAGES_URL}/profile/twitter.png" alt="{INPUT}" /></a>
* Input Mask => Regex
~[a-z][0-9a-z.-]{1,31}~i
Google+
* Wrap user input in text
<a target="_blank" href="{INPUT}"><img src="{DEFAULT_IMAGES_URL}/profile/gplus.png" alt="G+ profile" /></a>
* Input Mask => No HTML
LinkedIn
* Wrap user input in text
<a target="_blank" href="{INPUT}"><img src="{DEFAULT_IMAGES_URL}/profile/linkedin.png" alt="LinkedIn profile" /></a>
* Input Mask => No HTML
FB and Twitter are "Text 50".
G+ and LinkedIn are "Text 255"