|This tip comes in handy if you (oops!) put your hot iron down on the wrong side of fusible interfacing. It is also good to do just in general every once in awhile.
You can buy a kit called the Rowenta Soleplate Cleaning Kit (I got mine at JoAnn's, I think.) It is good for any brand of iron; it does not have to be a Rowenta.
Basically, you get a tube of goop and several different types of cloths. You squeeze the goop on a cotton terry cloth, and just iron over it with a hot dry iron. You will be amazed at the quantities of crud that come off of your iron. It can change the soleplate from almost black to silver.
Afterwards, the iron will glide more easily, and you will be rid of that pesky interfacing that was stuck on it.