Apart from McLaren's surprising pace, the current hot topic is again Red Bull's flexing front wing. Last year there were similar worries after which the FIA introduced a beefed up front wing flexing test at the Belgian GP. However, even with the changed test, Red Bull still appear to have a major advantage at high speeds, hence allowing Vettel and Webber to gain a massive amount of time through quick turns.
It is evident that Red Bull passes each and every test, but the team appear to have devised a new way to gain an advantage by allowing the nose cone to flex as well. As it bends down slightly, the front wing is tilted forward and moved closer to the ground, creating more downforce. In fact, the central part of the wing - which has a mandated shape and usually creates lift - can also create 'marginal' downforce when tilted.
Evidence of the flexing nose can be seen at the following video. Please look carefully at the nose camera position at top speed and after braking for the first corner.