Does your friend's 2011 have the optional roof rails? If so, any set of cross bars that fit your 2007 *should* fit his 2011. I would take both cars when buying them to make sure, but any set that attaches to OEM roof rails (i.e. Thule 450) should work.
Well, it is not true. 2007 and 2011 cross bars have different OEM numbers and the widths are different and so are the prices. I have just looked at Thule 450 on Amazon, and the foot pack itself costs $150 without the bars.
Sorry, never meant to talk about OEM bars, just third party (Thule, Yakima). So I should have written "If so, any set of 3rd party cross bars that fit your 2007 *should* fit his 2011."
The advantage of having a single set of bars is that you can just lift it off the car without having to remove and install the roof top box each time.