Prior to the 3.0 upgrade my 3G was jail broken using Pwnage, and unlocked using yellowsn0w. I also had a number of other Cydia apps installed. I tested the battery life by running SlingPlayer with the volume set at the lowest level and the iPhone positioned within a few feet of the wireless router. It lasted about 2 hours 20 minutes before the phone shut itself down. I upgraded to 3.0, using Pwnage to generate the requisite ipsw file to jail break the phone, and installed ultrasn0w and pretty much the same collection of Cydia apps as before. Again I tested the battery life with SlingPlayer but this time the iPhone was two floors away from the wireless router. Nevertheless it lasted a full 3 hours before shutting down. It isn't a very scientific test, but it is a reasonably fair comparison of before and after and shows around a one third increase in battery life when using a pretty CPU intensive app. Of course YMMV!