Hello, I'm torn between the 15 MBP and the 17, and am wondering if anybody uses the 17" on their lap for LONG periods of time (many hours). How do you find the 17's for weight, heat and maneuverability (sp?)? Comfortable? Bearable? Regrettable ... should have got the 15". If you find the 17" very comfortable on the lap, but you're the size of an NFL linebacker, please indicate! BTW, does the i7 run hotter or cooler than the i5? Thank you.