After updating to the rooted version of GB my battery lasts longer than it did in Froyo. I have seen people post other places about battery life... some good... some bad. I think it may have to do with what you have running on your phone.
Just wondering if anyone has figured anythign else out about this. I'm also getting a much higher "phone idle" portion of my battery drain after GB update. IN my case, over 25% and the #1 consumer of battery power. Used to alway be "display".