Task Killer is not needed and actually does more harm than good, I don't think there is any doubt about that anymore. I use Juice Defender for the reasons mclarryjr mentioned above, I'm not a heavy phone user and it sames me a ton of battery life. Juice Defender does essentially nothing for your phone while the screen is on and your phone is in use, but it has several good features (IMO) for when the screen is off. I got blasted for saying this in another thread the other day, but I rarely get less than 18 hours out of my stock battery and often get 24-26 hours before I hit 15% battery life. Like I said, I'm not typically a heavy user, most of the time spent checking twitter, FB, Google+, and email.