I have the latest 1.67 Powerbook (High Def screen), which takes DDR2. According to the specs, it's supposed to take 4200 DDR2 SDRAM, and I had 2 gigs in it. But I got 2 gigs of 3200 DDR2, and the computer seems much faster. Is this my imagination, or does the CPU actually address the faster memory faster? Has anyone actually tested this? Does 4200 DDR2 RAM slow down the newer Intel macs significantly?