Battery lasts from 6am to 11pm, and would even longer, but that is when I charge it over night.
On a typical working day, a few minutes of phone calling, moderate web surfing, up to 2 hours of playing music over FM transmitter, and being always online with 3G, pulling weather updates regularly.
My current firmware is OS 41-10. Battery life improved a lot with OS 39-x IMHO. Have been using the device since mid of September.