As noted in a different thread here, I had problems with the DS108J after the upgrade. Backing up to it from another Diskstation would fail, and after that I could no longer log in to the DS108J. It would report that my userid and password were incorrect, or that the disk was full and that a reboot was necessary.
Another issue that I noticed was when going in to the storage manager and doing a SMART test (the simple 2 minute one), it would stop at 90% and never finish.
I downgraded the firmware to 3.1-1594 and noticed that the problems didn't go away.
I have since downgraded again to 3.0-1354 (that's three point Oh), and the DS108J is now working as it should.
Let this be a warning for anyone out there with a DS108J