For all those who recently acquired a WET54G (rev 3.1), or are planning on acquiring one, should read the problem I had with it.
The problem only affects EU versions of the product, as the US version has a more recent firmware available which fixes the problem.

Update: there's still no new firmware. I've updated the links so they are correct again.
And here's a direct link is here.

Anyway, the main symptom is the lock up of the device as soon as a connection with a wireless network has been made, and that network uses WPA-PSK or WPA2-PSK. I've tested this out extensively  ...