I've only had it a couple of days, so I don't know what the normal usage life is going to be yet, but it looks to be fairly decent. I spent a couple hours at the pub using it to score darts and it spent most of the time on with the backlight running. Battery went from full to about 80% during that time. Sony says about 10-12 days on of normal usage on a charge. From what I can tell, that looks to be accurate.
One thing to note: my normal usage includes running the backlight. The screen in not really readable without it unless you are in bright light. It looks like it is an EL backlight though, so it should be pretty efficient. Time will tell.