So I've been beavering away on a system that dual (or triple) boots AND provides a local R/W storage partition that is accessible from each OS. Choosing a common filesystem is tough, though:
* EXT2/3 drive exists for Windows, but the only one available for Mac OS doesn't work properly, so that's out.
* HFS+ drivers exist for Linux, but the Windows one costs $40+/machine - too much
* FAT32 is crap for all kinds of reasons.
* NTFS drivers exist for Linux and Mac OS (NTFS-3G) but when I write a file to the NTFS data partition from Mac OS the data is gone on reboot - this not a good thing. I discovered that it is because NTFS-3G is a userspace filesystem it generates a UUID for the partition each time. I *think* this is why the data is toasted, but I don't find others complaining (why?).
* other, more exotic filesystems (JFS, ReiserFS, ZFS, UFS etc.) aren't supported well enough on ANY non-native operating system.

I conclude that this is not worth solving in the context of a lab setup. Here's one solution:
The new labs will require a server to store teaching materials. We can build an inexpensive machine (>$2000) with heaps of storage (~4TB) and multiple NICs, on a gigabit network. The machine will export NFS and SMB/CIFS shares that get picked up by Mac OS (NFS) and Windows (SMB/CIFS). This will provide very fast storage that is available from any machine in the domain.