For me
i always keep the Music player on ( i drive a lot ) so i hear my fav. music on the Radio ( using the FM Transmitter ) all the time.
and ofcourse the Phone app. and the Conv. app.

I feel the music player use lots of battery, and its kind of heavy
if nokia coiuld create a music player that play music without the need to lunch the Music player app. and to save some RAM and Battery
that would be great
ohh and the Phone App, if i didnt keep it running all the time
i feel when i get a phone call the phone will go slowly to start ringing and flipping the screen and all that.

and the phone does freez a lot
but still its my fav. phone ever