In reply to Jay2K: A lot of people get on well with softshells in winter, Having a high wind resistance or being wind proof is the most important thing imo. They all have varying amounts of wind resistance/proof ranging from fully windproof gore windstopper to a lesser resistance of something like polartec. Being beghaus if it's the windstopper or the AF fabric then they're both up to the job, you'll know yourself how windproof they are. As you say, a nice pair of long johns underneath and you'll be toasty.
The time when a fully waterproof pant is the best choice is probably if it's raining when you set off or you're going to be climbing wet ice or sitting in wet snow. Someone will be along shortly to recomend a pair of decathlon salopettes shortly....
Ben