I'm using the JIT optimised for the x10's family of processors, I think it is 2.2, and it is vastly better. However, as regards battery life, I didn't notice a significant drop, but it was pants anyway. However, what I did was remove the face recognition service and TiemScape and now a full charge will give me around 30-38 hours of moderate use. I also use the phone as an alarm clock so it just gets put into flight mode at night.
Unless you are particularly attached to either of these features, get rid of them and laugh at iPhone users for their paltry battery life ;-)
A