I can't say I've ever really noticed the letters, though I think I would remember any combination that seemed 'rude' or 'naughty. At least you can ready the bloody things on AW. Lots of sites, and not just 'adult' ones, use the 'captcha' system where the letters are so distorted they're just about impossible to read. I can't see that it makes any difference whether the letters are distorted or not; if the 'person' trying to get into a site is really as machine it won't be able to 'read' the letters either way.