4 and even 8-processor PMG4s are being tested at Infinite Loop, and at least one major third-party Apple hardware testing site has sent in extensive reports on a 600MHz/4-processor model. Reports have been very positive overall -- under OS X Beta, tester sources saw performance in Photoshop 6.0 as much as 65% faster than a quad-processor Windows2000 system using 1.1GHz Pentium III processors. Overall performance was a solid 40% faster.
Notice anything odd about that? Well first we have the fact that the 1.1GHz chips were recalled by Intel -- oh, and then there's the fact that PIII's in general are only capable of running in a dual configuration, not quad. The only chip Intel is currently producing that will go higher than 2-way SMP is the Xeon. Judging from these facts and the benchmark scores they reported, I have a feeling they're confusing quad 1.1GHz PIII's with quad 180MHz Pentium Pro's.