I'd love to have a unionfs, but my understanding is that no such beast exists for Linux 2.4 currently and won't likely appear until after the 2.6 release. If this is not the case, I would love to hear about it. Is there some decent (although maybe beta) support for a unionfs in the 2.5 kernels? I am using the LVM2 backport to 2.4 currently to test the device-mapper approach out in the meantime, but if there is a better way to do it, I'd love to hear about it.