I have being using Juice Defender on my Samsung Galaxy S 2 for 1 year by now and its doing a great job there, so once I got my hands on the Prime, I installed it there.
It didnt do any much difference, the Prime already manages the power surprisingly well. The battery lasts with me for about 2 days of heavy usage with torrent working most of the time.
But if you still wants to use it, I set the JD to the advanced mode, pretty much everything that come as default I didnt touch but I set to toggle the wireless at 10kbs/30 secs
The options that makes the big difference are Cell data stuff and we dont have it so not much what to do there anyway
I found setting the prime on power saving good enough though. IMHO what can help out the battery pushing it to last ever further is a custom firmware like Cyanogen which I hope to see it in the future. Or some small bug fixes from Asus.