Since I got my n1 I have wanted to remove the facebook, twitter and amazon mp3 app but as they are stock apps it would not let me. Its so annoying that they were running in the background and possibly using battery but it was even more annoying that when I selected a pic in the gallery app it would always have facebook and twitter in the share menu when I really wanted to just have estrip there. After rooting my phone which is really quite simple on a nexus 1 (you can find instructions by searching on google) you need to do this.
Make sure your phone is recognized with adb by typing
adb devices
Then run the following code. It basically mounts the system drive and then you move the apps to a backup file where they are there if you later change your mind, but they will no longer run.
To be fair I totally stole these commands from here

and then added Twitter and amazon mp3 store to it
su
mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system
cd /system/app
mv Facebook.apk Facebook.bak
mv com.amazon.mp3.apk com.amazon.mp3.bak
mv Twitter.apk Twitter.bak
mount -o ro,remount -t yaffs2 /dev/block/mtdblock3 /system
sync
down with facebook.............