In March of last year is when I first wrote about LLVM/Clang being toyed with for Debian. Nearly one year ago it was found that LLVM's C/C++ compiler was actually building much of the Debian archive while providing better compiler warnings/errors than GCC. The results were more positive than originally anticipated with less than 10% of the packages having problems being built with the alternative open-source compiler.
The Debian developers working on Clang support aren't doing so because they want to deprecate GCC but rather they want to provide their users with greater options and Clang does have some rather nice error/warnings (although GCC's reporting has improved recently too), static analysis tools, and other features to benefit developers. Pushing the packages through multiple compilers also generally ensures better code quality too.
In July was another LLVM/Clang update for Debian. It was reiterated the Clang work wasn't to wage some GPL vs. BSD war in the Debian camp but for technical reasons. With the code at that time, just over 10% of the Debian archive was having problems being built under the latest LLVM/Clang over GCC.
At FOSDEM 2013 last weekend was another presentation by Sylvestre Ledru on building Debian with LLVM/Clang. Embedded below is the WebM video of this presentation. For those just wanting build results and other technical details, visit clang.debian.net.