As an update to my last post regarding my hpmount debacle, I've found a pretty good solution for my problem. I've got a dual-boot Ubuntu/Windows desktop, which I almost always run in Ubuntu, a MacBookPro running OSX, and a LaCie external USB hard disk. I want to be able to share the disk across computers without the 4GB file size limitation of FAT32 and would ideally keep the disk running HFS+ since it is primarily to be used for my Mac. Windows compatibility would be a nice bonus, but isn't really a priority.

The simple answer is this. The disk can be formatted in HFS+, but journaling has to be disabled for Ubuntu to mount it read/write. This seems to be actually doable safely on the fly, such that the disk could normally be used journaled, as long as journaling is disabled prior to attempting to write to it from Ubuntu. This can be done from the command line as follows:

sudo /usr/sbin/diskutil disableJournal /Volumes/MyDisk

for a volume named MyDisk

After mounting and working with the disk normally in Ubuntu, journaling can be reenabled in on the Mac as follows:

sudo /usr/sbin/diskutil enableJournal /Volumes/MyDisk

Info found in the Apple docs.