One could lengthen battery time by underclocking and feeling lag all the time on 3g,3gs.

Have to edit fstab file through SSH ( i hope this is legal )

Google around u can find the tutorials.

I changed my iphone 3g to 600mhz maximum clock and 300 mhz idle clock.

Seems that the battery life is shortened . but its worth it for the performance

I've tried 600mhz , 100 idle . 8 hours of sleep. only 5% standby gone