The Ghost Whisperer/2 is impressively warm for its weight. Nevertheless, there are limits to its utility. The jacket really is a perfect outer layer for most three-season hiking conditions and will keep you comfortable right down to about freezing (when paired with a suitable base layer). Beyond 0°C (32°F), however, you risk losing precious body heat.
For winter hiking and frosty urban environments, the Ghost Whisperer makes an excellent mid-layer beneath a more heavy-duty parka.