Here are some quick-n-dirty performance results for template instantiation in Clang and GCC 4.2. The test is very simple: measure compilation time (-fsyntax-only) for a translation unit that computes the Nth Fibonacci number via a template metaprogram. Clang appears to be scaling linearly (or close to it) with the number of instantiations. And, although you can't see it in the chart, Clang is a little over 2x faster than GCC at the beginning (Fibonacci<100>).
Fibonacci.pdf (54.5 KB)