mine lasts for 20 - 24 hours

changes:
-no active widgets on desktop (apps that connect on the net)
-using 2.5G signal (for the whole 8 work hours and 2 school hours)
-wi-fi only at home
-brightness set to 1 (i like it better when dark)
-unchecked all boxes on setting > location (GPS)
-minimized rebooting as posible
-enable "power saving" (disables all options along with it)
-backlight time set to 30secs
-notification lights not active for "device on" and "others"

activities:
-2-3 hours of mp3 music
-online using 2.5G signal up to 10hrs straight (browsing, im, etc...)
-1 hour of games
-less than an hour of calls, 20-30 sms/mms

(on weekends with no school and work, power lasts for 8 hours, applied the changes above)