Originally Posted by Nexus_One
It's also a hell of a lot better than becoming a vampire. In Oblivion being a vampire was great because you could control how far along you were in the progression of the disease, so if you needed extra strength for looting or fighting a bigger battle you could sleep and let the disease progress. In Skyrim though the disease progresses on its own, regardless of whether or not you sleep. Once you get to be a full fledged vampire you're pretty much f@#$ed as no one, not even the one guy who can cure you will help you. They'll just all try to kill you instead, and your stamina and health and magic will all reduce greatly during the day.
When you feed, I believe it will still reset the 4 day progression.