I usually have a set of summer and winter wheels and tyres. My Golf came with Goodyear Vector All-Seasons (new tyres, used car).
They are *****. They are spongy (like winter tyres), struggle for traction in the hot summer (like winter tyres), struggle for traction in the wet (like winter tyres) and struggle for grip in cold, damp conditions (a bit like all crap tyres).
I am yet to test them in snow, but quite frankly I'm not holding out much hope.
Goodyear Vectors aren't the best all-season tyres, but they're hardly crap in the grand scheme of things. As stated a few times in this thread, all-season tyres seem to have all of the downsides of winter tyres, without many of the benefits :/