[...] Oh, and after 32 rw mounts, you need to use the hfpmount on it, which will fail but will allow the kernel to mount it. I use 2.6.7.
I had a similar problem: with the early 2.6 testingkernels I could write on the hfs+ volume just fine (also with 2.4 benh kernels after the new ardistech hfsplus code was merged iirc), yet suddenly it threw an error when I tried to mount it rw[1].
Running OS X fsck.hfsplus on it didnt change it yet your suggestion with hpmount/hpumount (in the debian package hfsplus ftr) fixed it. That was rather unexpected and I didn't make a copy of the first few sectors where the relevant bit was flipped so maybe mount or the kernel misses something upon unmounting an hfsplus volume?
-Thomas -- [1] # mount -t hfsplus /dev/hda2 /osx -o rw # mount | grep osx /dev/hda2 on /osx type hfsplus (rw) # dmesg | tail -1 HFS+-fs warning: Filesystem was not cleanly unmounted, running fsck.hfsplus is recommended. mounting read-only. # touch /osx/test touch: cannot touch `/osx/test': Read-only file system