Performance wise I've seen some good results from Clang SVN in the last few months. Not universally faster (or slower) than GCC or ICC, but I have seen (important, useful) cases where code was 30-50% faster compiled with Clang than anything else I tried. (I also saw cases that had terrible performance, and occasionally miscompiled code, though mostly it was +-10% of GCC).

I can't say I understand why anyone would care too much about compilation speed, though - GCC+ccache is about as fast as Clang+ccache, as the primary bottleneck is disk throughput.