You gotta love the Internet. Having a couple of large external hard disks myself (and having carted around a FAT32 disk for the last week), here's something I'd like an answer to myself: How to share external (USB or Firewire) disks among Windows, Mac OS X or Linux, preferably with a transactional filesystem and with large file support (i.e., around 40GB).
I can vouch for FAT32 working on both Windows and Mac OS X flawlessly - the disk that is travelling with me is a 120GB Maxtor, onto which I dumped a bunch of files from my XP server and which worked first time when I plugged it into my iBook's USB port. The only drawback (besides the iBook's lack of USB2) is Mac OS X's tendency to clutter the hard disk with .DS_Store files, but those are easy to remove.
But I keep wondering how I would re-format the disk if any trouble ocurred. Microsoft has a comprehensive list of the FAT32 limits, but it fails to mention the fact that, even after installation, the Disk Manager won't format a FAT32 partition bigger than 32GB.
Talk about forcing people to use NTFS...
The original question, it seems, will go unanswered. There is no standard/common filesystem that would work on all three platforms, nor a reasonable hope we'll get one soon. So we're stuck with FAT32 and slicing files below the 4GB-minus-one-byte limit. No transaction log, no encryption, no compression (that particular NTFS feature has saved me more than once from running out of disk space), but, worse of all, no way to format the blasted things larger than 32GB other than using a Windows 98 machine.
Update: I eventually found (and confirmed) a way to format FAT32 partitions in XP - Partition Magic 8.0, with which I reformatted a 120GB drive at a friend's house. It was either that or installing Windows 98 SE (which I kept when I threw away my old MSDN CDs). I'm still looking for freeware (and Mac OS X native) alternatives, though.