How fast do the fastest computers generate bitcoins?

I've noticed that hashing performance doesn't vary as much between CPUs as you'd expect.  Compared to an old CPU, a newer CPU doesn't show as much of a speedup at hashing as it does on general benchmarks.

I guess recent CPU optimizations must have concentrated on things like I/O and branch prediction.  Most programs are a bunch of memory access, comparisons and branching, they rarely get down to cranking away at maths for very long.

The latest SVN version has a khash/s display.  Around 400 khash/s per processor is typical.