Here's what the beta explanation looked like. I'm still working through how this will affect my habits (I retweet a lot) or the look of twitter streams in general. It has not rolled out to any third party clients, and I have only seen one RT in this format by someone else in the wild so far.
There's an invisible RT button that surfaces when your mouse hovers over it, in the same place where you reply to a tweet.
If you follow the person already, I'm not sure that you see the retweet. If you don't, it looks like a normal tweet, with the symbol, and a little message at the bottom. (See previous post).