I just got a 4S, and it seems noticeably worse than my 4 (which I only had for a few months after its initial release). It might just be that I've been playing with it more in the first week of owning it (coming off a year and a half with no smartphone), but the battery has consistently been down to 5% after 12 hours.
I've only had my iPhone 4S for a week, but I haven't noticed anything drastically worse than my iPhone 4.
It certainly hasn't ran out of power during the course of a day yet.