This winter, I burned about a half cord of sycamore that I had gotten from a neighbor's felled tree and split myself. It had seasoned for about a year and a half. Its performance was so-so.... it burned a little too quickly and didn't burn as hot as other wood I burned with it this winter (maple, black locust, oak, sweet gum). Given the opportunity again to get it for free, I would of course take it, but only in smaller quantities, as I was overall disappointed with it.
I agree with danrclem -- it was a pain to split, with a difficulty on par with splitting black locust and sweet gum.