My Quad has 16GB and at some point I decided that rather than having it sit there unused all the time I wanted to put it to work. I came up with a way to create an 8GB ram disk by creating four 2GB ram disks and then RAIDing them. It was useful to have my browser and cache in a ram disk as well as having Photoshop use it as a scratch disk.
My G5s also have 16 GB of RAM and I would have use cases for a RAM disk of that size. I’m curious - do you have a particular script for creating RAM disks and merging them or do you do that manually? If you do have a script, do you mind sharing it?