In reply to UKC Gear: Will makes some great points for the alpine climber - his speculation on why they might bite better on black ice than other tools is the type of thing that only comes from proper knarly experience!
I've climbed a few shorter routes with my friend's Cobras, but bought new Vipers myself last winter. In retrospect, I'm happy with my decision - from the perspective of a mid grade ice climber, I don't think the advantages of the Cobras outweigh for me the cost difference and also worries about longevity.
Something else Will doesn't mention is they make really weird noises! The carbon fibre is very different in feel and sound - for me it was like going from a steel framed bike to an aluminium one - although in the case it should be the other way around.