Two that I know of, one who boasts about being a business woman - are completely open about the fact that they aren't registered as they 'wouldn't earn enough to pay tax anyway'. That's how it works - is it? National Insurance, for a start.
I am a self employed marketing consultant and copywriter - and it really riles me to see these people setting up a Facebook page (selling dummy clips or 'candy'), painting themselves as the new Alan Sugar and then not declaring it!
I am not sure why it riles me so much to be honest, maybe I feel as though it makes a mockery of genuinely self employed people? Maybe it feels like they are taking the piss! During my first year of being self employed, I didn't earn enough to pay tax but I still declared it and paid my NI!