I usually add it to my summer to do list. ...and if we get a warm day or two "mid-winter," around January, I'll shut her down and give it a swab. Its always just a thin buildup of dry, crusty creosote that turns to dust when you swab the stack.
I burn seasoned hardwood: mostly maple and cherry, with a bit of ash, and oak. It's my primary heat source, so it burns nearly non-stop, late October through mid-April, give or take. I'm sure that helps to keep it clean.
