That Hangouts update from yesterday has one more trick up its sleeve, and it's an interesting one. Google has opted to change the behavior when you tap on a contact photo so it no longer tosses you to Google+, but opens a contact card like most other areas of the system.
It really didn't make a ton of sense to have the photo open the Google+ profile. Hangouts is a communication method, so seeing all a person's contact info seems reasonable. You can still get to the Google+ profile for most contacts by going to the web tab in the contact card, though.
Be aware, you won't actually get any popup for users who are only connected to you through Hangouts (i.e. not in your address book). This is a little counterintuitive, as the app just sits there due to the lack of a contact card. In this instance it might be nice to open the G+ profile just so it does something. At any rate, this makes the Hangouts app feel a bit more distinct from all the Google+ stuff.