A big thanks to Roman Zippel!
He has written read/write support, improved performance, and added simple (OSX style) resource fork handling for HFS+ in Linux. I'm in the process of merging his changes, but until I get a new patch released, you can download it from http://www.ardistech.com/hfsplus/
New patch available against the 2.4.18 kernel. Haven't had any stability problems, and runs pretty well on small drives, and reliable but somewhat slow on very large drives. Note that any hard links created in OSX will show up without their data, as they are handled in a somewhat strange fashion...
I've fixed it enough that I can read directories and data forks. I've uploaded a patch, and I can see it in the admin interface, but it doesn't seem to be available... I'll try to get that fixed.
I've got it to where I can compile and load a module, but it panics with a kernel BUG() immediately. I think I know what the problem is, and I'll try to fix it the next time I have a chance. As soon as I get anything that even remotely works, I'll start up a download entry for the current patch against a normal kernel tree so anyone who doesn't want to download the whole kernel out of CVS can try it.
My original try at providing HFS+ support for the Linux kernel is available, even though I don't intend to continue along the path I started. You can find it as an "Out of Date" patch in the listings.