I've had carb icing once while airborne in a PA28 on a hot summer's day. Engine just sounded rough and the yoke was vibrating, selection of carb heat cleared it in half a minute or so. Funnily enough I'd just done the FREDA checks a couple of minutes before as well.
I've had it on the ground a few times while waiting for the oil temeperature to warm up after start, that's in 152's, 172's and 28's.