Running daemons in the background happens all the time on Maemo... it's not a battery concern at all as long as your daemon isn't DOING a lot... i.e. if it's polling an accelerometer value once each second it shouldn't be a big deal... on the other hand, if part of the phone "idle mode" is to power down accellerometer then that might have an effect as the daemon would keep the accellerometer powered up. Won't know until somebody tries it...