I just wanted to pass the word along that JFS from IBM seems to have some serious problems.
I reformated my reiserfs partitions as jfs partitions and everything seemed well. Except recently, I rebooted my system for the first time since I started to use JFS and all of my partitions failed to mount. ( I changed fstab and all that ) I could mount the partitions read-only but no matter what I did, I just couldn't get it to read-write.
The wierdest thing was is that if I reformatted the partition, then I could mount, read and write to it. But as soon as I reboot, the problem starts again.
Needless to say, I went back to reiserfs. I just wished I would have stuck with it from the beginning.