I have noticed a significant increase in battery drain on my iPhone since updating it to 2.2. In fact with at least 75% of my battery life left, my iPhone drained to completely empty when left in sleep mode for 2 hours last night. In seaching the web for more information, I found this article on iLounge.com
Meanwhile, a separate group of users complaining of greatly reduced battery life are reporting standby times of less than 10 hours, but not all users appear to be experiencing the problem. In addition, a user claiming to be an iPhone developer has responded in a separate 2.2 battery life thread, claiming that the problem may be related to an issue with Safari, in which the iPhone fails to properly close its network connection upon exit, causing the device to physically heat up, and also leading to reduced battery life. In this instance, both the developer and other users claim that quitting Safari by holding down the home button has successfully restored their battery life.