A compact flash card _can_ be made to perform very well (I replaced the optical in a Macbook that I used as a car computer for awhile). the trick is to manually align the partition tables and filesystems to erase-block boundaries ie: 64k or higher. this is much more effective with old HFS than HFS+. by all means, disable journalling. I modified 10.4 init scripts to keep my ~library/cache on a ram drive. It was pretty usable... 10.5 has a distinct advantage in that you can disable filesystemaccess time (atime)