Ok, here's an update:
I've now taken the time to try the software out on Linux using Wine, and it was partially successful: I could install Adobe Digital Editions and authorize to my Adobe ID. (Had to use a direct link to download the Adobe software; it can't be installed from the normal link on their website).
I then downloaded the latest version of the Sony "Reader for PC" software (trying the version supplied on the reader itself failed to install) and installed that successfully under Wine. It even said that 'This computer has an authorised Adobe ID' or whatever under 'Help -> About'.
I could then go to the Store in the Reader for PC software and it displayed some links to Waterstones and WH Smith, which, when clicked on, opened up in a web browser. So far so good!
Unfortunately, neither Adobe DE nor Reader for PC will detect the Reader when running under Wine. So close and yet so far...
Very frustrating.
As a last resort, I changed my Readers region from UK to US, and tried to sign on to the Sony store directly over WiFi. I managed to create an account (I think), but after the last step it took ages and finally popped up some error message about the connection not being available (Code -1087), which is ridiculous since I definitely had an Internet Connection. Whenever I try to sign in again, I get the same error, although it will let me browse the store catalog.
The reader still says it's not registered with an Adobe ID though.
Sony definitely needs to provide a way to register the damn reader (excuse my language!) directly from the device! I may be in the minority as far as using a Linux PC is concerned, but what about people (esp. older people such as my grandparents) who may not have a PC at all?
Cheers,
- Micha.