With LLVM 3.1 also comes updates to Clang, DragonEgg, and other compiler component updates. The 3.1 cycle incorporates about six months of work from the Apple-sponsored team and others within the growing LLVM community.
Features of LLVM 3.1 are talked about in this article on Phoronix (there's also some test results linked from there). Plus there's also some unmentioned features there like AddressSanitizer (fast memory error detection), better support for VLIW targets, an ARM integrated assembler, MIPS64 support, support for the Qualcomm Hexagon VLIW CPU, and much more.
Find out more or download the LLVM 3.1 source-code by checking out the LLVM mailing list announcement.