I have a 3GS 32GB and I'm seeing startling improvements in battery life after installing OS4. I used to get about 5 hours of battery life a day previously. I had to buy a Mophie Juice Pack Air in order to get through the day (about 10 hours). With the old setup I was running a JB with SBSettings, Circuitous, backgrounder and a custom theme with Infinidock and Infiniboard...amongst others. Not a lot of cell usage but a lot of wi-fi. No bluetooth. Now I'm running OS4 JB but basically the bare bones. I haven't installed any Cydia apps or themes because I'm selling it on eBay. But the difference is staggering! I've been running with OS4 for about six hours and I'm still at 80%.... Besides losing all the Cydia stuff...I am also running the phone of the default standby mode...where the phone is going into standby in 60 seconds. Previously I had the stand by at 5 minutes. So this appears to be a big...big...power saver. I know I won't be able to live without my Cydia apps and JB with new iPhone 4 coming tomorrow. But I'm just amazed at the battery life without all the Cydia stuff. Going to have to seriously look at economizing my Cydia setups.