So far as I know (which admittedly probably isn't the most reliable when it comes to legal matters), everything stays on your record unless you manage to convince a judge to expunge it. Misdemeanors just aren't taken all that seriously by most, but there are some companies or situations that do care about them. Even the ones that don't take it that seriously might use it as a deciding factor when compared to someone who doesn't have such (or has fewer/less severe) issues on their record.