Hello Jacob,
Yes, the Contact's LinkedIn field is still in use. If the Contact has used the same email address on their Contact record and also for a certain Social Media site like LinkedIn, that information will pull into CRM. You will see that information in the Contact's Profile. The URL of the Contact's LinkedIn page will fill into the LinkedIn field, if that data was successfully connected. Each time you access the Contact's Profile page the Social Media information for the Contact will be refreshed.
All connections are based on the email address. The data returned for a Contact's social profile depends on many factors, including privacy settings and activity on social networks, as well as the match that can be made based on the data you have in your CRM. It is possible that social data may not be available for a Contact based on these factors.
Our article here shows where you can see the Contact's Profile: http://help.clickdimensions.com/individual-tracking-summary-profile-view/