On all detailed quotes. Just check below the heading of the quote saying "NEW Real-time" Yahoo help says "Real-time data shown on the quote summary page above the quote summary box is Electronic Communication Networks or ECN data. ECNs are electronic marketplaces that bring buy and sell orders together and match them with each other. The ECN Data provided on the Yahoo Finance site is powered by BATS Trading. Real-time ECN data is available for pre-market and market hours."
That's what island used to do - give away their book for free and let yahoo use their real time quotes - it helps them get more market share Same thing with BATS - smart move by the ECN
I've been using it for a few months now. The annoying thing is that it'll randomly stop working for upwards of an hour at times, and to get the most recent quotes you have to click the refresh button. When it does work it's great because you can have up to 200 tickers at a time instantly updating.