Besides LLVM 2.8's Clang C++ support now being feature-complete (Clang's C support was made feature-complete a few releases back), Clang also has support for Objective-C, introduces a libclang library, adds support for new architectures (SSE, ARM NEON, and Altivec), and has improved generated code quality, among other new work.
Besides the Clang improvements, there are a few enhancements to be found with DragonEgg (LLVM-GCC for GCC 4.5), VMKit, Compiler-RT, LLDB (the Low-Level Debugger), and the KLEE Symbolic Execution Virtual Machine. A few months back we reported on LLVM coming up with libc++ as a replacement to libstdc++ and with LLVM 2.8 this library is near feature complete, but still needs more love with Clang++. LLVM 2.8 also has now a drop-in system assembler, an ARM disassembler, ARM code-generation improvements, and better support for debugging optimized code.
The release notes for version 2.8 of the Low-Level Virtual Machine can be found at LLVM.org along with the in-depth release announcement. We already have benchmark results of LLVM 2.7 vs. LLVM 2.8 when being used by Gallium3D's LLVMpipe in the queue for publishing and now on our TODO list are C/C++ performance benchmarks for LLVM 2.7 vs. LLVM 2.8 vs. GCC.