I purchased juice defender ultimate after reading this thread and downloading the free edition to try. My initial assessment is that juice defender is quite useful if proper settings are used. Using the balanced profile seemed to only give a slight increase in power efficiency. Once I purchased ultimate, I adjusted the settings under "advanced" to turn on data connectivity when screen is on and to enable connectivity at regular intervals ( I set it to 5 minute intervals to check for texts/emails). With these settings, the impact to productivity and daily use is minimal. I have seen a jump in power efficiency that makes this investment worth my while imo.
As far as I can tell, if I went to the extreme and used a more aggressive profile, the power savings should increase, although extremely limited connectivity could delay receipt of important emails/messages.