How about this: performing the same actions on two iPhone 4 phones (one with iOS 5 and one with iOS 4) that are configured the same way and have the same applications running shows that the rate at which the battery gets used up on the phone with iOS 5 is roughly 1.5 - 2 times faster than that on the phone with iOS 4. And this isn't when just doing a quick test, but it's more or less continuously like that, based on a number of different comparisons over the past few days (if not a bit more).
It's actually noticeable when after a matter a few minutes (generally between 3 and 5) of using the iPhone 4 with iOS 5--simply doing basic things like checking for app updates, checking/reading email, browsing a few web sites, perhaps reading/sending a few text messages--goes down by 1%. It's actually fairly noticeable, whereas on the iPhone 4 with iOS 4 you don't really see the battery going down as often--you don't even really notice it under normal use, and it's not all that often even when you watch for it.
In terms of standby time, it seems like not much might have changed, at least not in a noticeable way (so far).
