i've heard of someone saying that they got 1 entire week of iPad usage, now that is truly amazing battery life!!!!
as for me I only measured my battery life once and it was ~7.5 hours at full brightness and ~9.5 hours at medium brightness.
after the update I did notice that my battery does die quicker then before, i hope apple fixes the problem soon. it seems like ever since I upgraded from version 3.~ I have issues with either WiFi or battery life. I mean seriously, can't those guys test their updates before they release them???