I'm using UDF for my LinuxOSX setting and it's awesome.

Ok everybody's occupied with surreal suggestions, but anyway:
*UDF* is quite awesome as a on disk format for LinuxOSX data exchange, because it has a file size limit around 128TB, supports all the posix permissions, hard and soft links and whatnots. There is a nice whitepaper summing it all up:
http://www.13thmonkey.org/documentation/UDF/UDF_whitepaper.pdf

If you want to use UDF on a hard disk, prepare it under linux:
1) Install uddftools
2) wipe the first few blocks of the hard disk, i.e. dd if=/dev/zero of=/dev/sdb bs=1k count=100
3) create the file system : mkudffs --media-type=hd --utf8 /dev/sdb (that's right, UDF takes the whole disk, now partitions)

If you plug this into OSX, the drive will show up as "LinuxUDF". I am using this setup for years to move data between linux and OSX machines.

I'm using a USB Disk formatted under linux with UDF (yep, it's not limited to DVDs, there is a profile for hard disks). It can be used without problems under OSX (even Snow Leopard)