Note that C++11 is apparently an "ongoing" project in gcc: Page Redirection - GNU Project - some features are listed as requiring 4.8, and I'm not sure whether 4.8 is working on AVRs or not.
The "Atmel AVR Toolchain", available for windows and linux, is now using avr-gcc 4.7.2 : http://www.atmel.com/tools/ATMELAVRTOOLCHAINFORWINDOWS.aspx
I compile with C++ 11 for many embbeded applications, without any problem (at all).
For AVR? Using gcc? Otherwise, it's a pretty meaningless statement.
"A newer version of the compiler" is a frequent request, since Arduino is stuck back at 4.3.2, which is quite old by now.
On the other hand, 4.4.x was broken, 4.5.x was broken, 4.6.0 was broken, 4.6.1 was broken... And 4.7 introduces a new mechanism for handling data in flash. (avr-gcc, avr-libc compiler and toolchain known bugs · Issue #1208 · arduino/Arduino · GitHub )
Perhaps the arduino team's reluctance to upgrade is somewhat understandable!