Last week, Google+ users started noticing an additional option in their "Contributor to" section: a past or current contributor drop-down. As of today, the option appears to be global. The "Contributor to" section is a requirement to establishing Google Authorship. Here, authors can list which blogs they contribute to. Now, authors can differentiate between blogs they actively write for, and those that they have previously contributed to, but not longer write for.
What This Means
This change may have Google Authorship and AuthorRank implications. By separating active contributions to past ones, it's possible that Google wishes to credit active publishing relationships over dormant ones. Unfortunately, it is unclear how much time constitutes a "past" contributor relationship.
Mike Arnesen has reported that the labels do change the rel="contributor" tags, with Current links appearing as rel="contributor-to", and Past links appearing as rel="past-contributor-to." It remains to be seen what, if any, impact this will have on the appearance of author rich snippets and content rankings. Google remains quiet on the issue.
What You Should Do Now
If you have Google Authorship established on any blogs, review your "Contributor to" section and label each link as either "current" or "past." If you aren't sure which to choose for any blog, ask yourself "Will I ever write for this blog again?" and "Has a significant amount of time passed since I last wrote for this blog?" Use your best judgment here.
If you haven't yet established Google Authorship through your Google+ profile, you can follow this guide to get started.
Iska Hain from the Google+ Communications team reached out to me to provide the following statement:
"We've made a minor improvement to the Google+ profile page so that now you can specify whether you're a past or current contributor to a given online publication. This way you can connect your Google+ profile with the content you've authored, even if you no longer write for a given site."