Figured I'd throw my two cents in. I bought this app last night and had my first full day with it today. For me, it's doing what is is supposed to do as far as switching between edge and 3G, and wifi and 3G. Have no complaints there. I'm still trying to figure out how much battery I'm saving, if any. At the end of my work day, I'm usually around 65-75% battery with light usage, usually checking email, sending texts etc. Today I was a little on the heavier side of that and I left work at 78% battery. So far, I have seen about a 5-10 percent increase in battery life. Right now I'm at 4:41 hours usage, 13:2 minutes of standby @ 37% battery life. Since I've got home, I've watched 2 5 minute videos on YouTube, and sent a bunch of texts and done a bunch of surfing. When I left work, I had about 1 hour of usage so the rest has been at home on wifi. I'll have to see how the next few days go, but so far, I like it.
It's not like you couldn't turn stuff on and off manually to increase battery life, but it's much better when it does it for you, lol. I usually just roll with wifi and 3G on, but now I dont have to. When I connect to a wifi source, it turns 3G off, and when I leave it, it will go to 3G, or turn it off if not in use.