You need to delete all your cookies/cache etc in the browser, then go to quidco, click the visit retailer to earn cashback link and buy the N900 through that. Sadly, it gives you no indication at all that it's working. But if you go to preferences>privacy>delete individual cookies on firefox, and start typing 'quidco' there should be a cookie from shop.nokia.co.uk that contains the word quidco amongst a load of random letters. If that's there then it has probably worked. Personally I noticed that it showed up on firefox but not chrome, so perhaps use firefox. Don't visit any other websites while you're doing it. I actually did it in a new firefox profile, because I was a bit paranoid that it wasn't working.