Been using SFS on my harddrive for several months now with Ibrowse no problems but my Cache and download directories are all on a separate partition for safety. Testing SFS and PFS found SFS to be much faster on my system with most things. BTW you can have both installed on your Hard drive.
Also make sure your first drive in the system has the newest version of SFS installed in the RDB otherwise things get messy. Master if ide or drive 0 if SCSI doesn't matter what the boot drive has on it as long as the first drive seen by the system has it installed.
kurt