In reply to Dom Whillans: I've got them. Them and nepals saw me through an alpine winter trip! Too warm for ski boots though in any condition I've been in so probably too warm for most double boots!
Haven't got any blisters in them either!
At home I use them as slippers, inside and out well.
The one downside to them is the entire sole is covered in synthetic insulation, constant compression=this failing rather quickly, but the rest of the sock is still warm, a decent insole is still needed though.
When these are eventually done, I shall buy another set.