Well I got my iPhone 4 about a week ago. When I got it I did several full charging cycles, 3-5 if I remember correctly. And these days an iPhone battery really seemed "unkillable". It was really hard ...
I've been impressed with the better battery time of my new iPhone 4 as compared to the 3G I had before. Yesterday evening, I finally jailbroke the 4, and the battery time today has been much worse ...