It does and it doesn't improve disk performance in slower Macs - from my experience using cheap CF cards (and ever cheaper PCMCIA adapters) booting and reading is faster, but writing definately isn't (especially lots of small files). But as mentioned the older the laptop, and going from a slow noisy stock HD, the CF card will make a more noticable improvement. I've taken to using PCMCIA CF adapters and CF cards as a universal "boot" device for all my Mac laptops (running OS 8.1 I think), and shoved in 10 - 30GB IDE drives into those capable that I've scrounged from old PC laptops.
JB