How much better is the battery life in the newest (2009) MBP 15"? The specs say that the non-user-replaceable battery is rated for 7 hours. I'm trying to decide between the newest 15" MBP and the previous generation. My current laptop, a Dell Vostro 1500, gives me about 2.5 hours which is usually sufficient most days. But, I do need to carry the AC adapter and have to occasionally plug it in to make it through my day. The 7 hours sounds great. But, is it *that* much better than the prior model? What's it rated at - 5 hours? Any real world results?