I have just purchased and configured one of these, partly on the basis of this review (I wasn't too worried about not being able to replace the discs). I want to note a few additional worries that might be useful for others:
1. The current web interface does not enable passwords with special characters, or passwords over a certain length (not sure exactly how much: 20 characters is too much, but 10 works). This dramatically reduces the security of the device out of the box. I've emailed LG to ask them to change this, and all they've said is that they will consider this for a future firmware release. I want to use TimeMachine over the internet, but won't be doing so until I can up the password security...
2. While this device is advertised as having an iTunes media server, it is subject to the massive problems that iTunes 10 has had with NAS media servers. See this thread for the problem: http://bit.ly/o96vKU —no idea whether this will be fixed anytime soon, as Apple have been totally unresponsive. So if you're planning to use iTunes with this as a media server, think again, or prepare to be very patient (of course, you can put media files on the NAS and then simply mount a drive).
3. The device allows FTP, but not SFTP. This is madness.
4. At present it is impossible to disable an SMB share from being broadcast on the network, even if you switch all drives to AFP only. The device seems to be sharing a directory "cdrom" that cannot be seen from anywhere else in the configuration software. This seems to be an artifact of the same basic setup being duplicated across this device and another that has an optical drive.