Vegas in February is relatively cold, but it's still full of Vegas-y fun. I've been once in late January, and we had a great time. You could walk outside comfortably during the day, but it cools down a lot at night so you'll definitely need a jacket. You obviously can't hang out by the pools, but there's still all the other stuff to do.

I've never really seen Vegas dead; there's always a ton of people from the L.A. area who drive up for the weekend.