FWIW, i've been running softdep on a 3000/400 with 2 tcds cards and about
13 disks attached.. all of the filesystems on these disks use softdep and
it has worked almost flawlessly for me.

the only flaw was due to an unrelated crash happening at the wrong moment,
or something.  i was running `rm -rf' on a $DESTDIR that had a full
NetBSD/sparc build in it at the time the crash happened.  when rebooting,
fsck found *thousands* of unreferenced files and proceeded to place them
in lost+found.  the problem is that there were too many files for
lost+found and eventually it gave up and had to mount the not-quite-clean
file system, remove/delete these files from lost+found, umount and then
re-fsck.  this second fsck completed (recoverying many more thousands of
files)... 

i didn't lose any data, it just was very annoying to recover from.  i've
not heard of anyone else experiencing this, either.