Hello, I'm currently on holiday in Orlando, I'm only here for two weeks, no intention of staying longer, I've just checked my passport and I've noticed the immigration officer has stamped the 15 august 2012 in my passport .. Should I contact them and explain?
Contact them to explain what? You have a stamp that allows you to stay in the US until August 15th. Doesn't mean you have to stay until then. You can leave anytime up to the 15th, but no longer. This is normal.
You are probably on the Visa Waiver Program? If you are part of one of the Countries that participates it gives you 90 days from the date you entered to leave. This would give you until August 15? Unsure when you entered the States.