A daunting question is always on my mind. I use my MBP 15" (the new one), as my primary machine in my office. I sit by my best usually 10-12hrs a day working on it. I am trying to figure out what is best to do, keep the AC plugged in or have it un-plugged and only plug it in when the battery is drained (or less then 50%)? I have tried different experiments, plugged in, not-plugged and time is about the same for life of the battery. The true question is, how is is best to do it for the health of the battery. I was even thinking, maybe its just a good idea to get the new iMac (when it comes out) and use that as my primary... dunno... Thoughts?