The design direction Google+ has been taking for the past year or so is the move towards circular-cropped profile photos, replacing the square thumbnails that were found everywhere across the board. Starting with photos on profiles/pages and shares on the stream (and even Hangouts for iOS), the trend has finally curbed square profile photos that appear on search results.
Whilst this is only a minor change, it shows that the Google+ team is focused on making the user interface polished down to the pixel, and that's fine by me.
Reported in our community by +Mohamed Magdy. Cheers!