Google is continuing to shine a brighter light on Hangouts users who are currently online. A few months ago the company brought back the green dot that used to mark online contacts in the days of Google Talk (which was replaced with a subtle green line in Hangouts). Going forward, the messenger in the web version of Gmail will contain a new tab that puts online contacts at the top. It's still possible to message friends who are offline, they're just tucked at the bottom where they're out of the way.
Many of us have contacts we want to keep at the top of the list regardless of their online status (a significant other, a good friend, maybe even a parent), so Google has also added the ability to pin people there. Just right-click and select the option.
This isn't the experimental Hangouts experience we discussed a couple of weeks ago, but it's still something new. The feature is rolling out over the next few days, so you may not have access to it just yet. I don't. Give us a holler in the comments if you do.