This is interesting, because the conventional wisdom of idiots on slashdot continues to be "use postgresql if you need advanced features, but use mysql if all you care about is speed," despite all the head-to-head benchmarks I've seen by third parties showing PostgreSQL to be faster under load. (MySQL's own benchmarks, of course, tend to favor their own product. Go figure, huh.)
Here's the latest, showing postgresql about 50% faster than mysql across a variety of hardware. But where MySQL really takes a pounding is when you add multiple cores / CPUs: MySQL adds 37% performance going from 1 to 4 cores; postgresql adds 226%. Ouch! (This would also explain why MySQL sucks so hard on the Niagra chip on the requests-per-second graph -- Sun sacrificed GHz to get more cores in.)
As even low-end servers start to go multicore this is going to be increasingly important.
Update: PostgreSQL core member Josh Berkus says :
[This] is a validation of the last four years of PostgreSQL performance engineering. It's not done yet ... if the Tweakers.net test had included 16+ core machines you'd have seen PostgreSQL topping out ... but our hackers have done quite well.