if you listen to long songs (i think around 10 minutes or more) your battery will die sooner.
The hard drive in the iPod isnt always on, it is active until it can copy around 10 to 15 minutes (maybe even 20) worth of songs to memory so it can play the songs using the smallest amount of power possible.
You can see this for yourself...Listen to around 15 seconds of a song, then go to the next song, then hit the fast forward thing a few more times. Your iPod will stall as it looks for the song on the hard drive and copies it so it can play the song for you.
As a result, if you listen to a long song, the hard drive will constantly be active sucking up battery power...
On the other hand, the length of time a battery can hold a charge will decrease as time goes on (look at all those battery complaints from 1g and 2g iPod owners

) and its a natural thing (those idiots are treating the iPod battery as though its a long lasting eternal thing, they wouldnt make the same fuss if they realized that the iPod battery is like a laptop battery...just as if not more expensive), so if that ever happens rest assured you can always open your iPod and replace the battery for a mere $80 or so.
Tips for making your iPod battery last:
dont use the backlight, or soundcheck. Set contrast to the minimum you can stand. The equalizer should be off, and the songs you should be listening to should be relatively short (a 20 minute long song will drain the battery).
Don't recharge it all the time, recharge when needed. Try not to play games and do half the stuff in the Extras folder. Once you listen to a song try not to change the song/volume as much as possible. Once you are done listening to your iPod, turn it off.

Good luck
