Juice Defender = Fancy Word for Task Killer
Sorry, but this is completely false. Have you even tried Juice Defender?
It is NOT a task killer. What it manages is the connectivity of your device to network data. If you always need your device connected to the network 100% of the time (because you need constant notifications from facebook, email, etc.) then JuiceDefender is not for you.
However, in its default configuration it will turn the network on every fifteen minutes to allow apps like your mail, facebook, etc. to sync and then will turn it back off. This is perfectly fine for me. It goes by your screen lock state. If your screen unlocked is on it does nothing, but when your screen locks and no app is running using data it will turn your mobile data off.
This saves a lot of battery and has a very noticeable affect for my battery life.
The only gotcha that I see is that when you unlock your phone sometimes it can take a couple of seconds to get reconnected to the network. So, for instance, say I want to check facebook -- I unlock my phone, hit my facebook shortcut and occasionally facebook will be trying to access the network before it is fully connected so you will get an error and have to exit out and go back into facebook. To me, that is a minor inconvenience for getting quite a few more hours of life out of my battery.
I use the free version and I must say it is getting me a noticeable gain on my battery life. Obviously to each his own, and if it doesn't work for you then don't use it. But it sure doesn't hurt to try installing it and using it for a week.