As I've not yet found the time to set up a mailing list, feel free to ask questions here.
I'll try to answer them and everyone else please try to answer them, too.
Is the TeraStation very loud?
The temperature regulated fan inside keeps the noise down, but the 4 hard disks produce a lot of vibration.
Are there any firmware updates?
There are no non Japanese firmware updates for the TeraStation at this time according to Buffalo tech support.
I want to avoid soldering. Is is possible to become root without serial console?
Creating your own firmware image with SSH installed and a known root password is possible. See here for a guide to extracting the firmware. Another method would be to remove the disks and modify them directly.
I don't want to open my TeraStation. Is it still possible to become root?
Yes. See the previous question regarding modifying a firmware image and applying it.
As it's possible to make your own (hacked) firmware, the old answers have been removed.
Has anyone successfully replaced the TeraStation's firmware with a different Linux system?
I've chrooted into a Debian/PPC. That works fine once you're root.
Can I install or replace Linux applications on the TeraStation?
No problem, once you're root.
Can I replace my existing 250GB hard drives with larger ones?
Kind of. You need some good knowledge of Linux Soft-RAID. But if you had that you probably would not have asked :-)
It might just work with the rescue mode of the 1.07 firmware but I don't have that firmware on my TeraStation, nor do I have enough money to get 4 bigger harddisks to give it a try.
Why sould I add a suduers file, can't I just change the root password?
No, the passwd file is backuped and restored during firmware update, so there is no point in changing the rootpassword in an update file.
The sudoers file is not backedup and restored, so you can becom root thisway.