@coderus: I found this hint in an ebay auktion for a N950 "Due to the use of different display technologies, on the N9, developers should avoid one pixel width fonts(?) and graphical objects with lines one pixel wide. Also avoid the extensive use of bright colors, especially white, when developing for OLED displays as this increases the power consumption (typical for OLED displays)."
Info for OLED: http://en.wikipedia.org/wiki/PenTile_Matrix_Family

If you are using a one pixel width line for battery status, there could be a little potential for optimization. ;-)