Yes, although as a Brit I see this as an Americanism, it's certainly not common usage here. I believe it's generally used when being invited to an event for exa

Yes, although as a Brit I see this as an Americanism, it's certainly not common usage here. I believe it's generally used when being invited to an event for example - "Do you want to come bowling with us on Friday?" "I'm down" However, it's not always interchangeable with "yes" - for example: "Did you get the server migration finished over the weekend?" "I'm down" ... Would be completely wrong.