It's a myth.
You'd have to literally eat a gob of fecal matter that happened to have a particularly high concentration of one of the virulent strains of salmonella to contract it. Usually when people see visible fecal matter on themselves, they don't put their fingers in their mouth or eyes.
This myth came about when little children were buying 1 inch turtles and PUTTING THE WHOLE TURTLE IN THEIR MOUTH, straight from their dirty water and likely scaring the poop out of them in the process - a HANDFUL got salmonella. We're talking about being more likely to die by slipping on a wet floor and hitting your head than salmonella from a reptile.
People get salmonella from produce or poultry. If you think that's odd, I urge you to explore the agricultural practices that are deemed acceptable in the US. I guarantee licking the cloaca of a terrestrial reptile living in a clean enclosure is less likely to give you salmonella than eating improperly prepared poultry or produce. You may say "I don't wash my produce all the time and I sometimes eat undercooked chicken or don't wash my hands after preparing chicken and I've never gotten salmonella." Exactly - the odds are even less than that for reptiles. The same can be said for e. coli - it's literally COVERING the surfaces in your kitchen and house - yet how often do you hear of poisoning? Companies that sell chemicals and people who lobby against pets create germ scares. If you want to mitigate risk in your life, get rid of your car. This is scientific fact - apologies for not choosing to take the time to find it in writing. Others in this thread seem to be well on their way to that, though. Thanks guys :)