Two thing that I've learned when using a laptop in coach:

1. Politely inform the person in front of you that you are using a laptop, and you don't mind if they recline...but please give me some notice!!

2. Use the laptop on your lap not the tray table. Most 15 inch screens will tend to catch just under the tray table latch and if the person in front of you suddenly reclines, your screen will snap like a twig! Had this happen a few years ago and unfortunately the computer needed a new screen. I ended up pitching it and getting a new computer.