The new Google+ layout is pretty nice, but if you're looking at it on a widescreen monitor it adds a lot of whitespace. If you'd like to cut down on that whitespace and centre everything, Whitespace Remover for Google Plus is a Chrome and Firefox extension that does just that.
Whitespace Remover doesn't overhaul or change the layout much. By default, Google+ has the navigation bar and stream on the left and leaves a ton of whitespace on the right. Whitespace Remover centres everything and adds a grey box around it all. Doing so cuts down on the brightness and makes it easier to look at on a widescreen monitor.