The way the 360 works is when you receive a "toast" you have until the toast message goes away to press the guide button, which then takes you directly to the friend that sent the message and your options regarding that message. The guide button on the controller is also flashing the toast as well, all in-game/media center/dashboard. The screenshot, pipo, used is not what one sees when they respond to a toast, it is the default guide screen.
The way EuroGamer worded it, it does not seem like they have a toast method as of yet on the PS3 service. It was worded as such that pressing the PS button would drop you from the game and then you could go to your message to read it.
It shouldn't drop you out of the game period as per the Untold Legends video - where possible it will pause the game and bring up a version of the XMB, which includes the friends list. What we're all wondering is if you can message etc. from there. If you can, then that's all fine and dandy. Access to your friends from within any game with in-game notifications of friends list 'events' is more than I'd have expected. But we'll see what comes..if you have to exit out of a game altogether to do any messaging, then I'm sure such functionality being available in-game will be top of their to-do list for OS updates.