Beware of the "it's never happened to me, so the law doesn't exist" know-it-alls. Facts are simple. If immigration don't like you or your immigration history, they will use it to deny entry. 99.9% of people it won't affect. If you're the 0.1% you're back on the plane to where you came from. And this only applies to tourism-based entries, not to non-imm visas. This is the page from the Washington Embassy website for the non-believers.