I have to admit that I had (probably) never heard of Black Friday until the other day, when it came up in the context of a special computer deal. According to Wikipedia, the UK has Amazon/Apple/ASDA propaganda to thank for the term. See here. Closer inspection of the Wikipedia sources reveals that the term is not so new after all – see here – but seems to have trouble catching on in the UK. Perhaps this calls for thanksgiving?
Shortly after I had written the above, I was alerted to the fact that the situation is in fact worse than it initially seemed. Apparently Amazon Germany call it "Cyber Monday Woche". Victor Meldrew comes to mind!
There is another Wikipedia article here, which indicates that Currys, PC World, Comet and Harrods are also 'culprits'. In any case, I'm not sure one could go as far as saying it is 'observed' in the UK. Note also the reference to 'Shopping' as a "Celebrations" category. Sick-bags, anyone?
Especially in view of the fact that tomorrow is supposed to be Buy Nothing Day UK! On a related note, see interesting forthcoming RSA event under the heading Why We’ve Had Enough of Stuff. Plus the Story of Stuff.