Permit me to demonstrate. If you're on a single processor Mac, going to Butterfly Labs (the reliable test case for this problem, though I'm sure there are others) is sluggish and beachballs a bit, though it eventually loads. My iMac G4 grinds into it after around 30 seconds, which is lousy, but bearable. Now do it on a multi processor Mac. On my 10.4 quad G5, it takes minutes despite having four times the cores, four times the L2 cache and 2.5 times the clock speed, even with processor performance set to Highest, during which the browser is unresponsive for long periods of time. That, to express it gently, sucks. After some exhaustive debugging I am fully convinced that this too is almost entirely due to inefficiencies in the Tiger kernel's implementation of pthreads. The processors just trip over each other trying to stay synced and the threads get starved for resources.
Other things. Now that Google has made Google Groups slow and hard to navigate, which I used to use for reading Mozilla newsgroups (though I guess that's better than what they did to Google Reader), I finally have an excuse to try Tenfourbird. Normally I read Usenet and E-mail from a shell prompt, but I decided to use Tenfourbird and talk to news.mozilla.org directly to see how well it works, and to keep those groups separate from my regular .newsrc file. And, well, wow. It's quick and fast, and seems pretty much bug-free. I am delighted to see that our anonymous builder in the land of the rising sun has kept pace with us, and I hope he makes the jump to 24 when we do. ありがとうございました。