myth in my opinion
i always have the coldest fucking hands even on not very cold days, and this past season i bought the grenade spring glove/spring mitten combo mitten's they make, and have never had warmer hands in my life
i think the combination of a spring glove inside of a mitten shell is the perfect combination, although kinda pricy ($80 for the ones i got) they are completely worth it. plus it's not like you spent $80 for only something you can use on frozen days. when it warms up you still have the spring gloves to use from march, on. i'd highly recommend checking out the grenade setup i'm talking about, you'll probably be pretty pleased with them.
check em out here: http://www.tactics.com/grenade/misfitten-gloves