Vinegar is the common name for acetic acid (I am a chemist). It is a weak acid, which is why it is a good cleaner, however it will do damage to fabrics in the long run. (same reason you don't want to use sharpies to write on fabric as they have acids in them, or need to buy acid free papers to store things in)
I just wanted everyone to know this before they go and spray vinegar on their fabrics. It would be fine to clean out your iron with, but I would wash it out with water before I pressed fabric with it. Just my 2 cents worth.