I like vests. I often get too hot wearing a heavy jacket when I tack or ride, so a vest fits perfectly. Though, I'm one of those people that when its 45, I'll be wearing a shirtsleeve shirt and normal breeches. I'm a little biased in the cool weather... I like to freeze!
I do like a jacket here and there, I have a horseware Ireland fleece jacket and it fits great and it's super soft, I just can't wear it riding. I have nice soft red vest (warm enough mostly) and I just bought a poofy horseware vest and I can't wait to wear it!