I hope this is not a silly question? But I'm interesting in buying a Tom Tom go live 540, and on some sites I've seen the letters HD after Tom Tom, but I don't see this on most sites including amazon who are the most reasonable in price! Is there a big difference whether it's HD or Not?
No, not a silly question at all. TomTom HD is a part of their Live subscription service. the first 3 months are free, thereafter about £8/month. Depending on how much you drive, you must ask yourself is it worth it.